You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
For the molecule named [(3S)-3-[6-(3-chlorophenyl)pyridin-2-yl]piperidin-1-yl]-(5-methyl-1H-pyrazol-4-yl)methanone by IUPAC nomenclature, provide its molecular formula.
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C21H21ClN4O
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