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:
nsnnsggngsgg

Ex Output:
snns


Ex Input:
uunufnffufununn

Ex Output:
unu


Ex Input:
kkkkzpzpzp

Ex Output:

zpzpz