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: fmmnnmmfmnfm
Example Output: fmmnnmmf

Example Input: gxxxcccggxggccc
Example Output: cccggxggccc

Example Input: gvvggvvgvvg
Example Output:
gvvggvvg