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

Example Input: fCGEhfHvcRouHzNw, gtjBkhfHvcRouHee
Example Output: hfHvcRouH

Example Input: bVlwKYBYmcNq, hBlwKYBprL
Example Output: lwKYB

Example Input: tIvPEAKDXfXMxvVXn, azzEAKDXfXMxCS
Example Output:
EAKDXfXMx