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:
yybbkyybybkykk

Ex Output:
yby


Ex Input:
yynnnyfnynyynyf

Ex Output:
ynyyny


Ex Input:
mmmjmmhjmjj

Ex Output:

mmjmm