You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
Translate the chemical IUPAC name N-ethyl-1-[7-(3-methoxyphenyl)-4-oxo-3H-thieno[3,2-d]pyrimidin-2-yl]piperidine-3-carboxamide into its molecular formula.
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C21H24N4O3S
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