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

Example Input: plSfJAktMfac, TCjYJAktlt
Example Output: JAkt

Example Input: RAmKlEAUfWcgF, ZlWfEAUfWvVRa
Example Output: EAUfW

Example Input: ptGYwbKmrRcnjGitW, JIfmTbKmrRcnjoLBW
Example Output:
bKmrRcnj