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

Example Input: OrcQOvMBhmwP, mnWrzcQOvMBnLwI
Example Output: cQOvMB

Example Input: DwkTGsIXLfmjMV, VqRlMxtsSBkTGsIXLfmjbvI
Example Output: kTGsIXLfmj

Example Input: cFKzkRHGl, NRXzkRHhfWe
Example Output:
zkRH