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

Example Input: DUhUbmfLuOFAQann, kwnzfLuOFAErR
Example Output: fLuOFA

Example Input: PivhPfah, XSghPfOi
Example Output: hPf

Example Input: IJvcGImLwirD, yBgwGImLDzD
Example Output:
GImL