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

[EX Q]: gWMyioGBRpwcXfr, AOQGBRpwcSccqBE
[EX A]: GBRpwc

[EX Q]: oCtWZYdkvZ, pkktWZYdEHMW
[EX A]: tWZYd

[EX Q]: Zrfiyfbv, KSTfiyJxD
[EX A]:
fiy