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

Example Input: OFbCjZDoRRlLsMU, DcCjZDoRRtld
Example Output: CjZDoRR

Example Input: UtUSmsOI, dCUSmGoQ
Example Output: USm

Example Input: IwOSjFNsIvjojoLUYNfN, TbUFNsIvjojoLEHEJXKsuH
Example Output:
FNsIvjojoL