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

Example Input: HorIyjpfBFmKZQUIEoP, AcWOaOgVPmyjpfBFmKZQPFYiI
Example Output: yjpfBFmKZQ

Example Input: HKCoXQsLRtowYJ, PGRzNUQsLRtoLcqkn
Example Output: QsLRto

Example Input: WtyWjEieXveHWPRD, AbRuqjEieXvrkMvh
Example Output:
jEieXv