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: aaarrrprrapaar

Output: rrprr


Input: Consider Input: woworororrwo

Output: ororo


Input: Consider Input: nbnnbvvvnbnvn


Output: vnbnv