You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
2-(6-chloro-2,3-dioxo-1,4-dihydrothieno[2,3-b]pyrazin-7-yl)acetonitrile The above is the IUPAC name of a molecule. Write its molecular formula.
user
C8H4ClN3O2S
assistant