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

Example Input: YlhtTQgHiffTbIbBrcHMqFKCdWz, HyregFgMffTbIbBrcHYUnnQvGlx
Example Output: ffTbIbBrcH

Example Input: PQCjJwXurLeN, vsjJwXuOy
Example Output: jJwXu

Example Input: iTQDuuzVdsZzeno, AEBCwdzQDuuzVdsWMZyzI
Example Output:
QDuuzVds