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

Example Input: UvYbfKFybXofcwLRrLRiK, BgMZKFybXofcVe
Example Output: KFybXofc

Example Input: lPhVhAQZWJDrvzcEaGEwKgZAuJI, qIJDrvzcEaGDRCRrB
Example Output: JDrvzcEaG

Example Input: fkdvancbQ, yPdvanPq
Example Output:
dvan