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

Example Input: lQwpMQRxuVbJDv, UkzwpMQRxuDVT
Example Output: wpMQRxu

Example Input: FQAznAuFjoBKRKB, hPmtFFPnuAznAuFjoBKTgkeJyjcd
Example Output: AznAuFjoBK

Example Input: XwDQGsisTccgRgpGVvuCkYRmZJUXw, WLIWwYMJXccgRgpGVvusYNw
Example Output:
ccgRgpGVvu