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:
yyusususussssuy

Ex Output:
usususu


Ex Input:
aaqaeaaeqqeq

Ex Output:
eaae


Ex Input:
vgfvgvffgfggv

Ex Output:

fvgvf