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

Example Input: OyrqfQQnzOFUzrkDM, iBkQQnzOFewhjvO
Example Output: QQnzOF

Example Input: oiNEYHxbvAb, bcDDdEYHxbCREd
Example Output: EYHxb

Example Input: UTdardKNThdYrGKMqZPeg, mvrThdYrGKMlcCxBtak
Example Output:
ThdYrGKM