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

Example Input: QlJnxO, BLJnCQ
Example Output: Jn

Example Input: uHGHiARtdJbuG, OdZmiARtdrhC
Example Output: iARtd

Example Input: CCcyrvub, qGyrvRL
Example Output:
yrv