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

Example Input: KKebLWQCQzVIojj, nxQCQzVIopD
Example Output: QCQzVIo

Example Input: lkFGXvTkKm, wwELXvTkcOnG
Example Output: XvTk

Example Input: JHjiTQMdMQCXAnxLUXZJs, WJZdMQCXAnxLUixzvQK
Example Output:
dMQCXAnxLU