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

Example Input: mmDhYqPJC, qThYqxW
Example Output: hYq

Example Input: jkGcUm, dxGcSI
Example Output: Gc

Example Input: GrHTHvDRusaXlPDPFtVGgwez, WYbPGHvDRusaXlPbZq
Example Output:
HvDRusaXlP