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: aiqZheFuLtXAGRCGNBTAX, ssnVdztXAGRCGNBTIqmSJLZcy
Example Output: tXAGRCGNBT

Example Input: xEPfAGtyZdHKxfADgjmq, bjtyZdHKxiUk
Example Output:
tyZdHKx