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

Example Input: faHRBWyXsYzYmHQyy, aHTyXsYzYeXBFV
Example Output: yXsYzY

Example Input: ezVsFayUPcrte, lfsFayUMPTqx
Example Output: sFayU

Example Input: CRfEGgeskaBeZLbtbQ, jHgeskaBeZcNHDs
Example Output:
geskaBeZ