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: YcgVJVACcQE, JsJVACcSz
Example Output: JVACc

Example Input: BHOLSS, ZjOLfG
Example Output:
OL