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: nzzznznznznzz
Example Output: zznznznznzz

Example Input: dddkdkdnknnk
Example Output: dkdkd

Example Input: bbbpllbppbplpl
Example Output:
bppb