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: uunufnffufununn
Example Output: unu

Example Input: vvwvvvvvvvv
Example Output: vvvvvvvv

Example Input: kkokqkkkkooqo
Example Output:
kkkk