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

Example Input: rszjOPpbXm, pnBujOPpWHz
Example Output: jOPp

Example Input: zeuyZKwvIOfx, BlmZKwvspUt
Example Output: ZKwv

Example Input: mudMOSNkGeANyvMIYdYD, GQGqKZPZdMOSNkGeAzNqPR
Example Output:
dMOSNkGeA