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

Example Input: zBxuZfJgYrlRSzkmAktO, YNMgYrlRSzklmBOH
Example Output: gYrlRSzk

Example Input: nFgMXUzpStDAybiwm, aNJrXUzpStDjp
Example Output: XUzpStD

Example Input: bpVolVBPD, IFXolVMQ
Example Output:
olV