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

Example Input: lQwpMQRxuVbJDv, UkzwpMQRxuDVT
Example Output: wpMQRxu

Example Input: Owbiay, exbime
Example Output: bi

Example Input: dVwPsj, OIwPKq
Example Output:
wP