In this task, you are given two strings A, B. Find the longest common substring in the strings A and B.

Ex Input:
wbFDXJQDQxQJzudOUlR, QEbsIDXJQDQxQsSYIutwU

Ex Output:
DXJQDQxQ

Ex Input:
ChKUlYUTQQBjZMZkgEed, lmQQBjZMZkgdEf

Ex Output:
QQBjZMZkg

Ex Input:
atDgsOWuP, UJMgsOrwj

Ex Output:
gsO