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: osmJJcZlDAXBgJFsJKa, rzPNlDAXBgJYrgXlH
Example Output: lDAXBgJ

Example Input: sQCsxqvXnagYicivLLVwAo, fKKtElvXnagYicvvHAma
Example Output:
vXnagYic