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

Example Input: ugDpSMRvHM, DDwSMRvxw
Example Output: SMRv

Example Input: TnHJcxtwcZ, XFdHJcxNKw
Example Output: HJcx

Example Input: SfdgRrIEvLwNzz, uhjkRrIEvLupwX
Example Output:
RrIEvL