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:
nnnnyyunyuyyuny

Ex Output:
nnnn


Ex Input:
asooassooasso

Ex Output:
oo


Ex Input:
ggaggaaaaagggg

Ex Output:

ggaaaaagg