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

Q: JIOKyo, oPOKsX

A: OK
****
Q: PQSFjlnU, kTSFjMUh

A: SFj
****
Q: gEcYiQbPX, JiFYiQyQ

A:
YiQ
****