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:
aazaatattzatz

Ex Output:
aazaa


Ex Input:
wwqjjjjwwwwqqq

Ex Output:
jjjj


Ex Input:
vwrwrvrvrwvr

Ex Output:

wrvrvrw