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

[EX Q]: tGBRASi, QABRAtL
[EX A]: BRA

[EX Q]: iYSNsY, HSSNhP
[EX A]: SN

[EX Q]: fFUhcWkAZhXUqL, aWZWkAZhXnVwwq
[EX A]:
WkAZhX