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-[(3S)-1-ethylsulfonylpiperidin-3-yl]-7-[(4-fluorophenyl)methyl]-4-methyl-5H-pyrrolo[2,3-d]pyrimidin-6-one by IUPAC nomenclature, provide its molecular formula.
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C21H25FN4O3S
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