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

Example Input: ATmVEtUuZOgsBUuL, UMUuZOgsBPVT
Example Output: UuZOgsB

Example Input: RpaZAvSnEBgGapIPQgw, wcwYsXvSnEBgGapIwoIWROB
Example Output: vSnEBgGapI

Example Input: YUUNlPfWwFI, dLlsUNlPfSA
Example Output:
UNlPf