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.

Input: Consider Input: sssrrkkrrrssrk

Output: rrkkrr


Input: Consider Input: llvvkvllkvkv

Output: vkv


Input: Consider Input: wgygwywyygg


Output: wgygw