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

Example Input: mOGzbnDXWnNurkBXtcqZ, NLahGzbnDXWnNYgMTOR
Example Output: GzbnDXWnN

Example Input: OVVkkdeHoFlyNROyCP, zFVUJbvkkdeHoFlysF
Example Output: kkdeHoFly

Example Input: uQIdYKOEzIzlOhZ, kGcHCeqdYKOEzIzAYtcmNR
Example Output:
dYKOEzIz