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

[EX Q]: QKlzsmHyBcC, snPtzsmHdMIv
[EX A]: zsmH

[EX Q]: PGjDRPDzGaBR, rpIJRPDzWi
[EX A]: RPDz

[EX Q]: RqQQXNmHaDCNHcJguzQsaB, qeTfQKDCNHcJguzgmmv
[EX A]:
DCNHcJguz