You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
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4-[(2,3-dimethoxyphenyl)methylamino]-N,N-diethyl-5-methylthieno[2,3-d]pyrimidine-6-carboxamide is the IUPAC name of a molecule. Please give its molecular formula.
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C21H26N4O3S
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