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]: XwBMFIV, SNLBMFZQ
[EX A]: BMF

[EX Q]: KHmJHhYSXLWuHmHEAZwsJ, BXQSXLWuHmyBAnN
[EX A]:
SXLWuHm