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: ztgtzzzzzgzz

Output: ztgtz


Input: Consider Input: yvgvvyvyvgg

Output: vyvyv


Input: Consider Input: nndnnnddnd


Output: nndnn