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.

Example Input: ttvsvvvssst
Example Output: svvvs

Example Input: kyokoooyyoyy
Example Output: yyoyy

Example Input: xzgxzgxxzxzxxx
Example Output:
xxzxzxx