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Name the molecular formula for the molecule established as 1-[4-[8-chloro-5-(4-chlorophenyl)-3,4,4a,9b-tetrahydro-1H-pyrido[4,3-b]indol-2-yl]butyl]piperidin-2-one using the IUPAC nomenclature.
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C26H31Cl2N3O
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