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

Example Input: NNpkdhvgT, BMkAkdhvrwV
Example Output: kdhv

Example Input: OVZxWYzAAxG, rStOxWYzJeoC
Example Output: xWYz

Example Input: HCaIxxWmAWYm, GmXZaIxxWLVIVy
Example Output:
aIxxW