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

Example Input: RtOkkgLvhgfGlX, vCOkgLvhzOa
Example Output: kgLvh

Example Input: oZZUNCUHtIiauDxQ, OdindZUNCUHtIiLQmWJJf
Example Output: ZUNCUHtIi

Example Input: qPSQXQdqoabiQgYGIJcmUlRo, wbYyZZXwqoabiQgYGAlE
Example Output:
qoabiQgYG