You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
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Convert the IUPAC name of a molecule (4aR,7aR)-4-(4-methoxyphenyl)-1-(3-methylbutyl)-6,6-dioxo-4a,5,7,7a-tetrahydro-2H-thieno[3,4-b]pyrazin-3-one into molecular formula.
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C18H26N2O4S
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