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

[EX Q]: spGRUmIYuGl, qkqRUmItqU
[EX A]: RUmI

[EX Q]: jsXHot, gtXHmB
[EX A]: XH

[EX Q]: QsEiKikBJoOCNqlvxUwvD, OMBJoOCNqlhRvj
[EX A]:
BJoOCNql