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

Example Input: fCGEhfHvcRouHzNw, gtjBkhfHvcRouHee
Example Output: hfHvcRouH

Example Input: jinzsW, SMnzaW
Example Output: nz

Example Input: BqkzANYvZBGbHVAG, yDNNYvZBGPer
Example Output:
NYvZBG