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

Example Input: iYSNsY, HSSNhP
Example Output: SN

Example Input: SQNzngllNbOkKDK, MijfNzngllNDfWge
Example Output: NzngllN

Example Input: lYZArZWBLKFnNyFb, xFokfrZWBLKFngtemU
Example Output:
rZWBLKFn