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

[EX Q]: EPUxsZtt, KgxsZuXM
[EX A]: xsZ

[EX Q]: HKCoXQsLRtowYJ, PGRzNUQsLRtoLcqkn
[EX A]: QsLRto

[EX Q]: GlAYDsKQoXy, IxDsKQuK
[EX A]:
DsKQ