## 1) Abridged problem statement

You are given a small Perl-like program operating on **string variables** and the function `substr`.  
Variables not initialized are empty strings.

`substr(s, offset[, count])`:
- `offset >= 0`: start at index `offset` from the beginning (0-based).
- `offset < 0`: start at `len(s) + offset` (counting from the end).
- If `count` is omitted: take to the end of the string.
- If `count >= 0`: take `count` characters.
- If `count < 0`: take everything **except** the last `-count` characters (i.e., end at `len(s)+count`).

The program lines can:
- `print(name);`
- `print(substr(...));`
- Assign variables: `name1 = name2;` or `name1 = substr(...);`
- Replace a substring: `substr(name1, ...) = name2;` or `= substr(...);`

All offsets/counts are guaranteed to describe a valid non-empty substring.  
Output exactly what each `print` prints, one line per print.

---

## 2) Detailed editorial (solution idea)

### Key observations
- The task is **simulation**: maintain a mapping `vars[name] -> string`.
- Only a few syntactic forms exist (6 types). After removing spaces, they become easy to distinguish by prefixes:
  - `print(...)`
  - `substr(...)=...`
  - `name=...`
- The main complexity is correctly implementing Perl-like `substr` semantics, including:
  - negative offsets,
  - omitted `count`,
  - negative `count`,
  - replacement where the new string length may differ.

### Parsing strategy
The provided solution uses a robust simplification:
1. **Read all non-blank lines** (ignoring lines that contain only whitespace).
2. The first `N` non-blank lines are initializations, the next `M` are program lines.
3. For each program line, **remove all spaces** (`' '`) to normalize it:
   - Note: this works because the program grammar guarantees no spaces inside variable names or keywords, and string literals appear only in initialization lines (handled separately).

### Data model
Use `map<string,string> vars`.
- Uninitialized variables default to `""`. In C++ `vars[name]` creates an empty string if missing, so it matches the statement.

### Implementing `substr`
Define helper:
`get_substr(str, offset, count, has_count)`:

Let `len = str.size()` and:
- `start = offset >= 0 ? offset : len + offset`
- Compute `end`:
  - if `!has_count`: `end = len`
  - else if `count >= 0`: `end = start + count`
  - else (count < 0): `end = len + count`  (leaves `-count` chars off the end)
Return `str.substr(start, end-start)`.

This exactly matches the statement’s definition.

### Replacing via `substr(...) = newstring`
For `substr(name1, ...) = rhs`:
1. Compute `start` and `end` for the substring in `vars[name1]` using the same logic as above.
2. Compute `new_value`:
   - If rhs is `substr(...)`, extract that substring.
   - Else rhs is a variable name; use `vars[rhs]`.
3. Replace:
   ```
   str = str[0:start] + new_value + str[end:len]
   ```
This handles different lengths automatically.

### Handling each statement type
After space stripping:
- **Print**
  - If argument begins with `substr(`: parse inner arguments and print substring.
  - Else print variable value.
- **Substring assignment** starts with `substr(`:
  - Parse LHS substring spec up to `)`.
  - Parse RHS (variable or substring).
  - Replace in-place.
- **Normal assignment** otherwise:
  - Split at `=`.
  - RHS can be `substr(` or variable; assign accordingly.

### Complexity
- At most 300 program lines; each string length ≤ 1000 during execution.
- Each operation is O(L) due to substring concatenations.
- Well within limits.

---

## 3) Provided C++ solution with detailed line-by-line comments

```cpp
#include <bits/stdc++.h>          // Pulls in essentially all standard headers (ICPC-style)
using namespace std;

// Debug-style output for pair (not used by the solution logic)
template<typename T1, typename T2>
ostream& operator<<(ostream& out, const pair<T1, T2>& x) {
    return out << x.first << ' ' << x.second;
}

// Debug-style input for pair (not used by the solution logic)
template<typename T1, typename T2>
istream& operator>>(istream& in, pair<T1, T2>& x) {
    return in >> x.first >> x.second;
}

// Debug-style input for vector (not used by the solution logic)
template<typename T>
istream& operator>>(istream& in, vector<T>& a) {
    for(auto& x: a) {
        in >> x;
    }
    return in;
};

// Debug-style output for vector (not used by the solution logic)
template<typename T>
ostream& operator<<(ostream& out, const vector<T>& a) {
    for(auto x: a) {
        out << x << ' ';
    }
    return out;
};

int n, m;                         // N init lines, M program lines
vector<string> init_lines, prog_lines; // Stores the lines after filtering blank lines
map<string, string> vars;         // Variable table: name -> current string value

// Reads input, filters out blank/whitespace-only lines, then splits into init/program parts
void read() {
    cin >> n >> m;                // Read counts
    cin.ignore();                 // Consume the remaining newline after m

    vector<string> all_lines;     // Will contain all non-blank lines in order
    string line;
    while(getline(cin, line)) {   // Read the rest of the file line by line
        bool blank = true;
        for(char c: line) {       // Check if line has any non-whitespace character
            if(c != ' ' && c != '\t' && c != '\r') {
                blank = false;
                break;
            }
        }
        if(!blank) {              // Keep only non-blank lines
            all_lines.push_back(line);
        }
    }

    // First n lines are initialization statements
    init_lines.assign(all_lines.begin(), all_lines.begin() + n);
    // Next m lines are program statements
    prog_lines.assign(all_lines.begin() + n, all_lines.begin() + n + m);
}

// Structure to hold parsed arguments of substr(name, offset[, count])
struct substr_args {
    string name;                  // variable name
    int offset;                   // offset argument
    int count;                    // count argument (meaningful only if has_count == true)
    bool has_count;               // whether count was present
};

// Parses the inside of substr(...): "name,offset" or "name,offset,count"
// Input is expected without spaces (they strip spaces before calling this)
substr_args parse_substr_args(const string& s) {
    int comma1 = s.find(',');             // first comma separates name from offset
    string name = s.substr(0, comma1);    // variable name
    string rest = s.substr(comma1 + 1);   // the remaining "offset" or "offset,count"
    int comma2 = rest.find(',');          // optional comma before count
    if(comma2 == (int)string::npos) {     // no count provided
        return {name, stoi(rest), 0, false};
    }
    // count provided
    return {
        name,
        stoi(rest.substr(0, comma2)),     // offset
        stoi(rest.substr(comma2 + 1)),    // count
        true
    };
}

// Implements Perl-like substring extraction according to the statement
string get_substr(const string& str, int offset, int count, bool has_count) {
    int len = (int)str.size();
    // start index: from beginning if offset>=0, from end if offset<0
    int start = offset >= 0 ? offset : len + offset;

    int end; // end is exclusive
    if(!has_count) {              // substr(str, offset) -> to end
        end = len;
    } else if(count >= 0) {       // substr(str, offset, count) -> fixed length
        end = start + count;
    } else {                      // count < 0 -> leave -count characters off the end
        end = len + count;
    }

    // Standard C++ substring with (pos, length)
    return str.substr(start, end - start);
}

// Removes spaces ' ' from a string (note: does not remove tabs, but input uses spaces)
string strip_spaces(const string& s) {
    string result;
    for(char c: s) {
        if(c != ' ') {            // remove only normal spaces
            result += c;
        }
    }
    return result;
}

void solve() {
    // Parse initialization lines: $name = "value";
    for(auto& line: init_lines) {
        int dollar = (int)line.find('$'); // variables start with '$'
        int i = dollar;
        string name;

        // Read variable name: alnum, '$', or '_' (as per statement)
        while(i < (int)line.size() &&
              (isalnum((unsigned char)line[i]) || line[i] == '$' || line[i] == '_')) {
            name += line[i++];
        }

        // Extract quoted value
        int q1 = (int)line.find('"');     // first quote
        int q2 = (int)line.rfind('"');    // last quote
        vars[name] = line.substr(q1 + 1, q2 - q1 - 1); // store value without quotes
    }

    // Execute each program line
    for(auto& raw_line: prog_lines) {
        string line = strip_spaces(raw_line); // normalize by removing spaces
        if(line.empty() || line == ";") {     // ignore empty/degenerate lines
            continue;
        }

        // Case 1 & 2: print(...)
        if(line.substr(0, 6) == "print(") {
            // Extract content between "print(" and ");"
            string content = line.substr(6, line.size() - 8);

            // print(substr(...))
            if(content.substr(0, 7) == "substr(") {
                string inner = content.substr(7, content.size() - 8); // inside substr(...)
                auto [name, offset, count, has_count] = parse_substr_args(inner);
                cout << get_substr(vars[name], offset, count, has_count) << "\n";
            } else {
                // print(variable)
                cout << vars[content] << "\n";
            }

        // Case 5 & 6: substr(name1, ...)=...
        } else if(line.substr(0, 7) == "substr(") {
            int close_paren = (int)line.find(')'); // end of LHS substr(...)
            string lhs_inner = line.substr(7, close_paren - 7); // inside LHS substr(...)

            // RHS begins after ")=" and ends before ';'
            string rhs = line.substr(close_paren + 2, line.size() - close_paren - 3);

            // Parse LHS substring spec
            auto [name1, offset1, count1, has_count1] = parse_substr_args(lhs_inner);

            // Compute RHS value (either variable or substring)
            string new_value;
            if(rhs.substr(0, 7) == "substr(") {
                string rhs_inner = rhs.substr(7, rhs.size() - 8);
                auto [name2, offset2, count2, has_count2] = parse_substr_args(rhs_inner);
                new_value = get_substr(vars[name2], offset2, count2, has_count2);
            } else {
                new_value = vars[rhs];
            }

            // Perform replacement in vars[name1]
            string& str = vars[name1];        // reference so we modify in-place
            int len = (int)str.size();
            int start = offset1 >= 0 ? offset1 : len + offset1;

            int end; // exclusive
            if(!has_count1) {
                end = len;
            } else if(count1 >= 0) {
                end = start + count1;
            } else {
                end = len + count1;
            }

            // Replace substring [start, end) with new_value
            str = str.substr(0, start) + new_value + str.substr(end);

        // Case 3 & 4: name1=...
        } else {
            int eq = (int)line.find('=');
            string lhs = line.substr(0, eq);                         // left variable name
            string rhs = line.substr(eq + 1, line.size() - eq - 2);  // right side without ';'

            // name1 = substr(...)
            if(rhs.substr(0, 7) == "substr(") {
                string rhs_inner = rhs.substr(7, rhs.size() - 8);
                auto [name2, offset2, count2, has_count2] = parse_substr_args(rhs_inner);
                vars[lhs] = get_substr(vars[name2], offset2, count2, has_count2);
            } else {
                // name1 = name2
                vars[lhs] = vars[rhs];
            }
        }
    }
}

int main() {
    ios_base::sync_with_stdio(false); // fast IO
    cin.tie(nullptr);                // untie cin/cout

    int T = 1;                       // single test
    // cin >> T;                      // (not used)
    for(int test = 1; test <= T; test++) {
        read();
        solve();
    }
    return 0;
}
```

---

## 4) Python solution (same approach, detailed comments)

```python
import sys

def strip_spaces(s: str) -> str:
    # Match the C++ behavior: remove only normal spaces, not tabs.
    return s.replace(" ", "")

def parse_substr_args(s: str):
    # s is inside substr(...), with spaces already removed:
    # "name,offset" or "name,offset,count"
    comma1 = s.find(",")
    name = s[:comma1]
    rest = s[comma1 + 1:]

    comma2 = rest.find(",")
    if comma2 == -1:
        return name, int(rest), 0, False
    offset = int(rest[:comma2])
    count = int(rest[comma2 + 1:])
    return name, offset, count, True

def get_substr(st: str, offset: int, count: int, has_count: bool) -> str:
    # Implements the statement's substring semantics
    n = len(st)
    start = offset if offset >= 0 else n + offset

    if not has_count:
        end = n
    elif count >= 0:
        end = start + count
    else:
        end = n + count  # leave -count chars off the end

    return st[start:end]

def main():
    data = sys.stdin.read().splitlines()
    if not data:
        return

    # First line: N M
    first = data[0].split()
    n = int(first[0])
    m = int(first[1])

    # Collect all non-blank lines after the first line (blank = only whitespace)
    all_lines = []
    for line in data[1:]:
        if any(c not in " \t\r" for c in line):
            all_lines.append(line)

    init_lines = all_lines[:n]
    prog_lines = all_lines[n:n+m]

    # Variable table; missing variables are empty strings
    vars = {}

    # Parse initializations: $name = "value";
    for line in init_lines:
        # Find variable name starting at '$'
        d = line.find("$")
        i = d
        name_chars = []
        while i < len(line) and (line[i].isalnum() or line[i] in "$_"):
            name_chars.append(line[i])
            i += 1
        name = "".join(name_chars)

        # Extract text between the first and last double quote
        q1 = line.find('"')
        q2 = line.rfind('"')
        vars[name] = line[q1 + 1:q2]

    out_lines = []

    for raw in prog_lines:
        line = strip_spaces(raw)
        if not line or line == ";":
            continue

        if line.startswith("print("):
            # content between print( and );
            content = line[6:-2]

            if content.startswith("substr("):
                inner = content[7:-1]
                name, offset, count, has_count = parse_substr_args(inner)
                st = vars.get(name, "")
                out_lines.append(get_substr(st, offset, count, has_count))
            else:
                out_lines.append(vars.get(content, ""))

        elif line.startswith("substr("):
            # LHS: substr(...)=...
            close = line.find(")")
            lhs_inner = line[7:close]                 # inside lhs substr(...)
            rhs = line[close + 2:-1]                  # after ")=" up to ';'

            name1, offset1, count1, has_count1 = parse_substr_args(lhs_inner)

            # Evaluate RHS expression to a string
            if rhs.startswith("substr("):
                rhs_inner = rhs[7:-1]
                name2, offset2, count2, has_count2 = parse_substr_args(rhs_inner)
                new_value = get_substr(vars.get(name2, ""), offset2, count2, has_count2)
            else:
                new_value = vars.get(rhs, "")

            # Replace substring in vars[name1]
            st = vars.get(name1, "")
            nlen = len(st)
            start = offset1 if offset1 >= 0 else nlen + offset1

            if not has_count1:
                end = nlen
            elif count1 >= 0:
                end = start + count1
            else:
                end = nlen + count1

            vars[name1] = st[:start] + new_value + st[end:]

        else:
            # Assignment: name1=...
            eq = line.find("=")
            lhs = line[:eq]
            rhs = line[eq + 1:-1]  # strip trailing ';'

            if rhs.startswith("substr("):
                rhs_inner = rhs[7:-1]
                name2, offset2, count2, has_count2 = parse_substr_args(rhs_inner)
                vars[lhs] = get_substr(vars.get(name2, ""), offset2, count2, has_count2)
            else:
                vars[lhs] = vars.get(rhs, "")

    sys.stdout.write("\n".join(out_lines))

if __name__ == "__main__":
    main()
```

---

## 5) Compressed editorial

Normalize each program line by removing spaces, then simulate execution with a `name -> string` map.  
Implement `substr(s, o[,c])` by converting `o` to `start` (`o>=0 ? o : len+o`) and computing `end` as: to end if `c` missing, `start+c` if `c>=0`, else `len+c`. Extraction is `s[start:end]`.  
For replacement `substr(x,...)=y`, compute `[start,end)` in `x` and set `x = x[:start] + value(y) + x[end:]`, where `value(y)` is either a variable’s string or a `substr(...)` result.  
Handle three top-level forms: `print(...)`, `substr(...)=...`, and `name=...`. Output on each `print`.