You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
Translate the chemical IUPAC name (2S,4aR,7aS)-4-(3,5-dimethylphenyl)-2-(2-methylpropyl)-6,6-dioxo-1,2,4a,5,7,7a-hexahydrothieno[3,4-b]pyrazin-3-one into its molecular formula.
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C18H26N2O3S
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