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:
slusssllluls

Ex Output:
sss


Ex Input:
tbpptbtbttpbp

Ex Output:
tbtbt


Ex Input:
yqwqqyyyywwy

Ex Output:

yyyy