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

Example Input: fVEFJa, WtEFYK
Example Output: EF

Example Input: KKrCLvJKRoyV, WDeLvJKCBdS
Example Output: LvJK

Example Input: BslzmhpoXXvr, QGDzmhpoDUZzn
Example Output:
zmhpo