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

Example Input: spGRUmIYuGl, qkqRUmItqU
Example Output: RUmI

Example Input: OFbCjZDoRRlLsMU, DcCjZDoRRtld
Example Output: CjZDoRR

Example Input: LrVRrEiCOhgqhysEAmBbzqQ, tildRrEiCOhgqhSwtgswzFJq
Example Output:
RrEiCOhgqh