You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
For the molecule named 2-(3,4,6,7,8,8a-hexahydro-1H-pyrrolo[1,2-a]pyrazin-2-yl)-4-amino-5-propanoylthiophene-3-carbonitrile by IUPAC nomenclature, provide its molecular formula.
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C15H20N4OS
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