In this task you will be given a string and you should find the longest substring that is a palindrome. A palindrome is a string that is the same backwards as it is forwards. If the shortest possible palindrome is length 1 you should return the first character.

Input: Consider Input: nnqnqqnnnn

Output: nqqn


Input: Consider Input: txxttppxpxtttxt

Output: xtttx


Input: Consider Input: rrrkrkklrrkl


Output: rrr