You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
Provide the molecular formula for the IUPAC named substance [(4aR,7aS)-6,6-dioxo-1-propyl-2,3,4a,5,7,7a-hexahydrothieno[3,4-b]pyrazin-4-yl]-(1-ethylindol-5-yl)methanone .
user
C20H27N3O3S
assistant