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:
nwwnnzwnzzzzwnz

Ex Output:
nwwn


Ex Input:
yyunyuynuny

Ex Output:
unyuynu


Ex Input:
uuuuruuurrruuu

Ex Output:

uuurrruuu