You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
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For the molecule named (9aS)-2-(3-thiophen-3-ylpropanoyl)-1,3,4,7,8,9a-hexahydropyrazino[1,2-a]pyrazine-6,9-dione by IUPAC nomenclature, provide its molecular formula.
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C14H17N3O3S
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