You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
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6-[(4-ethoxyphenyl)methyl]-2-pyrrolidin-1-yl-7,8-dihydro-5H-pyrido[4,3-d]pyrimidine is the IUPAC name of a molecule. Please give its molecular formula.
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C20H26N4O
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