You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
2-ethoxyethyl 2-[5-(4-nitrophenyl)-4-oxothieno[2,3-d]pyrimidin-3-yl]acetate The above is the IUPAC name of a molecule. Write its molecular formula.
user
C18H17N3O6S
assistant