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

Example Input: DwkTGsIXLfmjMV, VqRlMxtsSBkTGsIXLfmjbvI
Example Output: kTGsIXLfmj

Example Input: RyaNyUvXAaZHLXUtYuz, CkbsWxZyUvXAaZHLXJJzugDy
Example Output: yUvXAaZHLX

Example Input: IiTlDImlGQbvIJ, PpFImlGQbvocSc
Example Output:
ImlGQbv