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

Example Input: kIBDjQLEZepVNHqnKqhine, hTZepVNHqnYTajyzv
Example Output: ZepVNHqn

Example Input: lLxXqKscqizXTO, TqrKscqizutDudo
Example Output: Kscqiz

Example Input: QqtCFzXHPNFXx, XECFzXHPSGwUuk
Example Output:
CFzXHP