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

Example Input: slTUxy, oqTUYa
Example Output: TU

Example Input: HorIyjpfBFmKZQUIEoP, AcWOaOgVPmyjpfBFmKZQPFYiI
Example Output: yjpfBFmKZQ

Example Input: AJytQj, JvytSS
Example Output:
yt