## 1. Abridged Problem Statement

You are given the full text of a problem statement consisting of sentences ending with `.` (dot). Words are separated by single spaces; there is no space before a dot.

You may create alternative versions of the statement by applying exactly one negation in exactly one place:

- Insert the word `not` (exactly this lowercase spelling) after any word equal (case-insensitive) to `can`, `may`, `must`, `should`.
- Insert the word `no` (exactly this lowercase spelling) after any word equal (case-insensitive) to `is`, `are`. If immediately after that `is/are` there is an article `a` or `the` (case-insensitive), you must remove that article.

For every possible single negation (in natural order: sentence by sentence, and within a sentence from left to right), output the modified sentence (preserving original word casing for copied words). First output the number of such sentences, then list them, one per line.

Input size ≤ 1024 bytes.

---

## 2. Detailed Editorial

### Observations

- We must consider each sentence independently, but output all possibilities across the whole text.
- Only one negation is applied per output line.
- Candidate insertion positions are determined by matching specific trigger words/phrases case-insensitively:
  - `can/may/must/should` → insert `"not"` after that word.
  - `is/are` → insert `"no"` after that word, and possibly delete the next word if it is `a` or `the`.
- We must not change the spelling/case of the original words we output (except inserting the new word which must be exactly `not` or `no`).

### Step-by-step approach

1. **Read entire input text**: the input may contain newlines, but logically it's a single stream of characters. Read all lines with `getline` and concatenate them with a space between lines.

2. **Split into sentences**: sentences end at `.`. Iterate over all characters and accumulate into `cur` until you meet `.`; then push `cur` to `sentences` and clear `cur`. The dot is not part of the sentence words; we will re-add it in output.

3. **Split each sentence into words**: use whitespace splitting (e.g., `istringstream`) to obtain `words[]`.

4. **Scan for insertion points**: for each word position `i`:
   - If `words[i]` lowercased is in `{can, may, must, should}`: create an output sentence by copying words `[0..i]`, adding `"not"`, then copying words `[i+1..end)`.
   - Else if `words[i]` lowercased is in `{is, are}`: create an output sentence by copying words `[0..i]`, adding `"no"`, optionally skipping the next word if it is `a` or `the`, then copying the rest.

5. **Output**: print the total number of generated sentences. For each generated word list, print words separated by single spaces and a `.` at the end. Order is naturally maintained because we process sentences in order, and within each sentence from left to right.

### Complexity

Input size is at most 1024 bytes, so everything is tiny. Time: O(total_words); Memory: O(total_words).

---

## 3. C++ Solution

```cpp
#include <bits/stdc++.h>

using namespace std;

template<typename T1, typename T2>
ostream& operator<<(ostream& out, const pair<T1, T2>& x) {
    return out << x.first << ' ' << x.second;
}

template<typename T1, typename T2>
istream& operator>>(istream& in, pair<T1, T2>& x) {
    return in >> x.first >> x.second;
}

template<typename T>
istream& operator>>(istream& in, vector<T>& a) {
    for(auto& x: a) {
        in >> x;
    }
    return in;
};

template<typename T>
ostream& operator<<(ostream& out, const vector<T>& a) {
    for(auto x: a) {
        out << x << ' ';
    }
    return out;
};

string text;

string lower(const string& s) {
    string res;
    for(char c: s) {
        res += tolower(c);
    }
    return res;
}

vector<string> split_words(const string& s) {
    istringstream is(s);
    vector<string> res;
    string w;
    while(is >> w) {
        res.push_back(w);
    }
    return res;
}

void read() {
    string line;
    while(getline(cin, line)) {
        if(!text.empty() && text.back() != ' ') {
            text += ' ';
        }
        text += line;
    }
}

void solve() {
    // This is a fairly simple problem, with a somewhat convoluted problem
    // statement. We simply split the text into sentences by '.', for each
    // sentence find words matching "can/may/must/should" (insert "not") or
    // "is/are" (insert "no" and remove following "a/the" if that's the case).
    // Then we can just output all candidates.

    auto is_not_word = [](const string& s) {
        string lo = lower(s);
        return lo == "can" || lo == "may" || lo == "must" || lo == "should";
    };
    auto is_no_word = [](const string& s) {
        string lo = lower(s);
        return lo == "is" || lo == "are";
    };
    auto is_a_or_the = [](const string& s) {
        string lo = lower(s);
        return lo == "a" || lo == "the";
    };

    vector<string> sentences;
    string cur;
    for(char c: text) {
        if(c == '.') {
            sentences.push_back(cur);
            cur.clear();
        } else {
            cur += c;
        }
    }

    vector<vector<string>> results;
    for(auto& sent: sentences) {
        auto words = split_words(sent);
        int n = words.size();
        for(int i = 0; i < n; i++) {
            if(!is_not_word(words[i]) && !is_no_word(words[i])) {
                continue;
            }

            vector<string> out(words.begin(), words.begin() + i + 1);
            bool no = is_no_word(words[i]);
            out.push_back(no ? "no" : "not");
            int start = i + 1;
            start += (no && start < n && is_a_or_the(words[start]));
            out.insert(out.end(), words.begin() + start, words.end());
            results.push_back(out);
        }
    }

    cout << results.size() << '\n';
    for(auto& r: results) {
        for(int i = 0; i < (int)r.size(); i++) {
            cout << r[i];
            if(i + 1 == (int)r.size()) {
                cout << '.';
            } else {
                cout << ' ';
            }
        }
        cout << '\n';
    }
}

int main() {
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);

    int T = 1;
    // cin >> T;
    for(int test = 1; test <= T; test++) {
        read();
        solve();
    }

    return 0;
}
```

---

## 4. Python Solution

```python
import sys


def solve() -> None:
    lines = sys.stdin.read().splitlines()
    text = " ".join(lines)

    def is_not_word(w: str) -> bool:
        return w.lower() in ("can", "may", "must", "should")

    def is_no_word(w: str) -> bool:
        return w.lower() in ("is", "are")

    def is_article(w: str) -> bool:
        return w.lower() in ("a", "the")

    sentences = []
    cur = []
    for ch in text:
        if ch == ".":
            sentences.append("".join(cur))
            cur = []
        else:
            cur.append(ch)

    results = []

    for sent in sentences:
        words = sent.split()
        n = len(words)

        for i in range(n):
            if not (is_not_word(words[i]) or is_no_word(words[i])):
                continue

            out = words[: i + 1]

            if is_no_word(words[i]):
                out.append("no")
                start = i + 1
                if start < n and is_article(words[start]):
                    start += 1
                out.extend(words[start:])
            else:
                out.append("not")
                out.extend(words[i + 1:])

            results.append(out)

    sys.stdout.write(str(len(results)) + "\n")
    for words in results:
        sys.stdout.write(" ".join(words) + ".\n")


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

---

## 5. Compressed Editorial

Read the whole input as one text string, split it into sentences by `.`. For each sentence, split by spaces into words. For every position `i`, if `words[i]` (case-insensitive) is `can/may/must/should`, output a variant inserting `"not"` after it. If it is `is/are`, output a variant inserting `"no"` after it and, if the next word is `a/the` (case-insensitive), skip that word. Preserve original casing of copied words, print one sentence per line ending with `.`. Output count first. Order is ensured by scanning sentences in order and positions left-to-right.
