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

Example Input: TnHJcxtwcZ, XFdHJcxNKw
Example Output: HJcx

Example Input: PQSFjlnU, kTSFjMUh
Example Output: SFj

Example Input: zvKqWGGZOuV, devYfWGGZOdvOg
Example Output:
WGGZO