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: vnbvnvbnnvbn

Output: nbvnvbn


Input: Consider Input: kvvnvnnnnkvn

Output: nnnn


Input: Consider Input: hhhhhhhphppppp


Output: hhhhhhh