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

[EX Q]: zfUPUDeKbCMQa, BkAJFJUDeKbCMZmkFu
[EX A]: UDeKbCM

[EX Q]: AxRSlkQfWHrdlgQG, iXIOrmlkQfWHTy
[EX A]: lkQfWH

[EX Q]: QDwJKM, lkwJSl
[EX A]:
wJ