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: nnngggununngnn
Example Output: nngnn

Example Input: yuppyyyuypyup
Example Output: uypyu

Example Input: yorrrryyoyoooy
Example Output:
yoooy