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:
ykmmkkmkmyy

Ex Output:
kmmk


Ex Input:
tggggtgtgttgtgg

Ex Output:
gtgttgtg


Ex Input:
vvvvvvvvvllvvv

Ex Output:

vvvvvvvvv