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

Example Input: sEYtoQlG, XIstoQQPw
Example Output: toQ

Example Input: lPhVhAQZWJDrvzcEaGEwKgZAuJI, qIJDrvzcEaGDRCRrB
Example Output: JDrvzcEaG

Example Input: wgwQzzaEZshTlHmksC, CgPXaEZshTlHldWmq
Example Output:
aEZshTlH