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

[EX Q]: JIOKyo, oPOKsX
[EX A]: OK

[EX Q]: lkFGXvTkKm, wwELXvTkcOnG
[EX A]: XvTk

[EX Q]: xczxnHODxupVcxr, EPnHODxuAvxcZ
[EX A]:
nHODxu