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

Example Input: XjYkMfARxWBSBjuXyDrFt, EtUxIfiHkMfARxWBSckTLTTnR
Example Output: kMfARxWBS

Example Input: NNpkdhvgT, BMkAkdhvrwV
Example Output: kdhv

Example Input: MguwwnwhxdTorGWcoL, OpMzhxdTorGGINKdoS
Example Output:
hxdTorG