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

[EX Q]: rvLoiycpZw, idcvoiycpcLyD
[EX A]: oiycp

[EX Q]: KfjqnJLciTXqkJK, yqfRcfqnJLcisSB
[EX A]: qnJLci

[EX Q]: jXCOPL, jVCOYZ
[EX A]:
CO