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:
vvtvtvvvvt

Ex Output:
vvtvtvv


Ex Input:
sssossocoo

Ex Output:
ssoss


Ex Input:
mkmkkkkkkokmmom

Ex Output:

kkkkkk