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

Example Input: aeQjEeiWGONmzGimhGiw, RIEeiWGONmOZuVYr
Example Output: EeiWGONm

Example Input: mOGzbnDXWnNurkBXtcqZ, NLahGzbnDXWnNYgMTOR
Example Output: GzbnDXWnN

Example Input: YsHnrq, gzHnAN
Example Output:
Hn