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

Example Input: HhBhJMpxpty, MxTJMpxnQEf
Example Output: JMpx

Example Input: lsNwypFwhKP, diEfLwypFwEKqCN
Example Output: wypFw

Example Input: kXmcLOvzFLbFjpUaXpQvbyehyYrFk, yOBIyGSrbFjpUaXpQvFMJ
Example Output:
bFjpUaXpQv