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

Answer: Yk


Question: BUvWkxrAvDQG, rHrkxrAkCE

Answer: kxrA


Question: LbRQqRfik, enoRQqRfSCOu

Answer:
RQqRf