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: QECPAHsg, bUfPAHOWb
Example Output: PAH

Example Input: FwcyPvNtEvGwdCdg, OYopezvNtEvGevuYLy
Example Output:
vNtEvG