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

Example Input: tWJoKSOAuVhmsomA, emdmnBFJoKSOAuVzSgW
Example Output: JoKSOAuV

Example Input: KKrCLvJKRoyV, WDeLvJKCBdS
Example Output: LvJK

Example Input: QkJyUX, QFJyTl
Example Output:
Jy