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: tztzxzxtzxtzzt

Output: tzzt


Input: Consider Input: kkoeekoookeo

Output: ekoooke


Input: Consider Input: kcvvckcccvkk


Output: kcvvck