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

Input: Consider Input: ZRjPgqbLL, uIsmPgqbBB

Output: Pgqb

Input: Consider Input: cCDTMXjGMNikONun, jpcMXjGMNizBEWQzT

Output: MXjGMNi

Input: Consider Input: Xhfsid, UYfswN
Output: fs