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

[EX Q]: CUlMsvov, iflMsSRp
[EX A]: lMs

[EX Q]: PQSFjlnU, kTSFjMUh
[EX A]: SFj

[EX Q]: gteQafv, wGNeQaCXz
[EX A]:
eQa