You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
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N-(4-chlorophenyl)-2-[2,4-dioxo-3-(pyridin-4-ylmethyl)pyrido[2,3-d]pyrimidin-8-yl]acetamide is the IUPAC name of a molecule. Please give its molecular formula.
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C21H16ClN5O3
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