You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
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For the molecule named (2,4-dichlorophenyl)-[(2R)-4-(2-fluoro-4-nitrophenyl)-2-methylpiperazin-1-yl]methanone by IUPAC nomenclature, provide its molecular formula.
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C18H16Cl2FN3O3
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