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

Example Input: DUhUbmfLuOFAQann, kwnzfLuOFAErR
Example Output: fLuOFA

Example Input: nXVXIEGP, fkXIEkU
Example Output: XIE

Example Input: ZcvVThdTt, efSxmvVThdIth
Example Output:
vVThd