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

Example Input: fdxgzAMP, xrcxgzYW
Example Output: xgz

Example Input: QECPAHsg, bUfPAHOWb
Example Output: PAH

Example Input: FkEbBEoIYlOjDXdV, WWKbBEoIYlOjROopmWhiT
Example Output:
bBEoIYlOj