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

Example Input: atDgsOWuP, UJMgsOrwj
Example Output: gsO

Example Input: zqwhMdAdXQfQCAmVNaYZm, toYMIwQeadAdXQfQCAmLyheFOv
Example Output: dAdXQfQCAm

Example Input: RNTCDHafSWgGmYnjKmtxKpu, PUPyNkKcSWgGmYnjBBgOh
Example Output:
SWgGmYnj