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: RNYHvcNnbsUdJLvS, PpNnbsUdglWhl
Example Output: NnbsUd

Example Input: yHUIpfKiGde, AEDpfKixbT
Example Output:
pfKi