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: ppuppuuupuppupp
Example Output: puppup

Example Input: rruoooourru
Example Output: rruoooourr

Example Input: asooassooasso
Example Output:
oo