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

Example Input: AxRSlkQfWHrdlgQG, iXIOrmlkQfWHTy
Example Output: lkQfWH

Example Input: njzfcapS, JDzfcYQh
Example Output: zfc

Example Input: vMLHpnXZnUJ, kuSZRNLHpnXZiT
Example Output:
LHpnXZ