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

Example Input: IIbJjQKWaoGKHGgWPcy, uNoMWaoGKHGqbnjmYQ
Example Output: WaoGKHG

Example Input: JjEQVKijeyEQ, dwSVKijeywCTvb
Example Output: VKijey

Example Input: HzySBq, sSySgC
Example Output:
yS