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

Example Input: OgWFOfjNYmXVjBBvOdunIc, eGljKGnzFKFOfjNYmXVjdlqsT
Example Output: FOfjNYmXVj

Example Input: slTUxy, oqTUYa
Example Output: TU

Example Input: XBigNTkPEtxKHQTZ, msNTkPEtxKwyZVNmE
Example Output:
NTkPEtxK