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: yiKkIxbKvNk, znaIxbKggg
Example Output: IxbK

Example Input: qylilQNUKNLlsajNZTEnSoitGJBDq, kUiwgueNLlsajNZTEpImHYONnM
Example Output:
NLlsajNZTE