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

Example Input: aZcGMvzBhazkCIFqpVe, AOljBvzBhazkWXeTuA
Example Output: vzBhazk

Example Input: RAmKlEAUfWcgF, ZlWfEAUfWvVRa
Example Output: EAUfW

Example Input: GhKHsQECvBZ, UnOHsQEUt
Example Output:
HsQE