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

[EX Q]: zBxuZfJgYrlRSzkmAktO, YNMgYrlRSzklmBOH
[EX A]: gYrlRSzk

[EX Q]: oZNKLmfxecDfkXEGFkRBYk, tReqkiExecDfkXEGtNZpJVRxC
[EX A]: xecDfkXEG

[EX Q]: aqYYOApRzjaNJrOrIlc, PdXDODdbiYOApRzjaNtSZ
[EX A]:
YOApRzjaN