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

Example Input: rlBoVyFsYqpmmQmelGBg, iKKaIyFsYqpmmWcrKn
Example Output: yFsYqpmm

Example Input: ZhHtTXaUmsQfUMNrnt, KvvebSXaUmsQfBspwM
Example Output: XaUmsQf

Example Input: dZVeumIekwKBkDbJyjZaoIjQlTl, QorAHVCwKBkDbJyjkscKdd
Example Output:
wKBkDbJyj