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

Example Input: Owbiay, exbime
Example Output: bi

Example Input: IIbJjQKWaoGKHGgWPcy, uNoMWaoGKHGqbnjmYQ
Example Output: WaoGKHG

Example Input: lzTmIqKpCAbl, MCqkqKpCApGHXr
Example Output:
qKpCA