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

Example Input: GrvtMjEvRlmN, ifGOWMjEvRPSOZK
Example Output: MjEvR

Example Input: XqyPjqNZDEK, EfwPjqNgjIP
Example Output: PjqN

Example Input: ARFpziNDSTezjOFhRa, fINDSTezjywlT
Example Output:
NDSTezj