327. Yet Another Palindrome
Time limit per test: 0.25 second(s)
Memory limit: 65536 kilobytes
input: standard
output: standard



You are given N words. Find the shortest palindrome (a word that is the same with its reverse) containing all of them as contiguous substrings.

Input
The first line of input contains an integer N, 1 ≤ N ≤ 14. The next N lines contain one word each, between 1 and 30 characters long. All the characters are small English letters ('a' through 'z').

Output
Output the required palindrome. If there're several possible solutions, output any.

Example(s)
sample input
sample output
1
avtobus
avtobusubotva

sample input
sample output
3
bacd
edcab
cabac
