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]: jXbgnl, lUbglP
[EX A]: bg

[EX Q]: pIZvCPIZCcPnnTpkX, ydagTXMiPIZCcPnnTCBVZUjlg
[EX A]:
PIZCcPnnT