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: BrDGrTD, PBHDGrDw
Example Output: DGr

Example Input: SCGCphG, HzYGCpvEG
Example Output:
GCp