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: pfppfvpppppff
Example Output: ppppp

Example Input: xwawwwxwwawaww
Example Output: wwawaww

Example Input: wawwxxxwaa
Example Output:
wxxxw