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.

Example Input: mmmmmmmbmbbb
Example Output: mmmmmmm

Example Input: kgttktgktgk
Example Output: tkt

Example Input: rmgrrggmmg
Example Output:
grrg

