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: dReySjyqecU, loSjyqiRl
Example Output: Sjyq

Example Input: FKuDbSKCLViRZE, YmbSKCLViNphQLAJ
Example Output:
bSKCLVi