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

Example Input: OYERnjubLFovtcS, FngzQJVGERnjubLFafmzq
Example Output: ERnjubLF

Example Input: RtOkkgLvhgfGlX, vCOkgLvhzOa
Example Output: kgLvh

Example Input: fdxgzAMP, xrcxgzYW
Example Output:
xgz