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

[EX Q]: OyrqfQQnzOFUzrkDM, iBkQQnzOFewhjvO
[EX A]: QQnzOF

[EX Q]: cxYVucnmEQopeWHrPJ, jNnOaYVucnmEQoSE
[EX A]: YVucnmEQo

[EX Q]: rJaPOFLuTeJwsPHNhvu, OKPDzHrVOFLuTeJwsDwO
[EX A]:
OFLuTeJws