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.

Ex Input:
yyllyylhyyyl

Ex Output:
yyllyy


Ex Input:
xnnxxxxnxx

Ex Output:
nxxxxn


Ex Input:
bkbbbkoobobobbk

Ex Output:

kbbbk