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.

Ex Input:
xxmxxmmmmmm

Ex Output:
mmmmmm


Ex Input:
snnynnnyyy

Ex Output:
nnynn


Ex Input:
kpkktpptktkt

Ex Output:

ktpptk