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

Example Input: qMnjlfIsQRtUlPggCpHqu, gfVndMwYDIsQRtUlPgqBJKCX
Example Output: IsQRtUlPg

Example Input: lPhVhAQZWJDrvzcEaGEwKgZAuJI, qIJDrvzcEaGDRCRrB
Example Output: JDrvzcEaG

Example Input: lfrpWrrJzglVLaWmvadSYQT, ZNhvDGsJzglVLaWmKIQkkp
Example Output:
JzglVLaWm