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

Example Input: ZhHtTXaUmsQfUMNrnt, KvvebSXaUmsQfBspwM
Example Output: XaUmsQf

Example Input: SQNzngllNbOkKDK, MijfNzngllNDfWge
Example Output: NzngllN

Example Input: tyedYS, XPedIP
Example Output:
ed