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:
pucuppppupu

Ex Output:
uppppu


Ex Input:
kkkkmmkmkk

Ex Output:
kkkk


Ex Input:
mvtvvmttvmttvtt

Ex Output:

ttvtt