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: ARGchkRez, kUwchkZPE

Answer: chk


Question: srPyjmTQhdFFMcQ, QQGBdtyjmTQhmfEy

Answer: yjmTQh


Question: tCeGnRBckpBUui, epFcrnRBckpBXhUn

Answer:
nRBckpB