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

PGjDRPDzGaBR, rpIJRPDzWi
RPDz

xfZYYDKEqoRRu, ztCeYYDKEqoPG
YYDKEqo

faPdPZJBxOJfijr, ZFbKZJBxOJfGKuurtM

ZJBxOJf