You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
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Under IUPAC nomenclature, a molecule named 1-[(4aS,7aR)-6,6-dioxo-2,3,4a,5,7,7a-hexahydro-1H-thieno[3,4-b]pyrazin-4-yl]-2-(2-pyrrolidin-1-ylphenoxy)ethanone is given. What is its corresponding molecular formula?
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C18H25N3O4S
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