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: MriFNpGM, yaiFNduk
Example Output: iFN

Example Input: ZGMHBeIrWgcfTQWTCl, gqNHBtGBeIrWgcfTQxad
Example Output:
BeIrWgcfTQ