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: hhhmmmmmmshhm
Example Output: mmmmmm

Example Input: gggzggzzzbggzzb
Example Output: ggzgg

Example Input: fnfpfppnnfppp
Example Output:
fnf