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

Example Input: rqhQxQQDdYwemFiiwcfVx, cEQDdYwemFtwpfNJC
Example Output: QDdYwemF

Example Input: vytthSjj, XVttthSFAvk
Example Output: tthS

Example Input: gROronOVdSWFnevaqeZBfJkG, FgBVdSWFnevaHZ
Example Output:
VdSWFneva