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

Example Input: RAmKlEAUfWcgF, ZlWfEAUfWvVRa
Example Output: EAUfW

Example Input: esIMEOgV, tNIMEybb
Example Output: IME

Example Input: FXBfmvYRzsrjrhDIg, EoJxJRvYRzsrOkjR
Example Output:
vYRzsr