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: tdtedtettddee
Example Output: tdt

Example Input: iwdiwdwwdi
Example Output: dwwd

Example Input: vyyyvvyyyyyyy
Example Output:
yyyvvyyy