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

Example Input: ezVsFayUPcrte, lfsFayUMPTqx
Example Output: sFayU

Example Input: SQNzngllNbOkKDK, MijfNzngllNDfWge
Example Output: NzngllN

Example Input: aRXTWw, oYXTqR
Example Output:
XT