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: sEYtoQlG, XIstoQQPw

A: toQ
****
Q: HvGYyrbGUFGAA, tAYyrbGBj

A:
YyrbG
****