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

Example Input: uHGHiARtdJbuG, OdZmiARtdrhC
Example Output: iARtd

Example Input: CMrTXnTnTVaR, srnXnTnTDNULO
Example Output: XnTnT

Example Input: YdrjkCCmdWwppePviLA, tzsyRtQYAmdWwppePvypqEAtH
Example Output:
mdWwppePv