You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
ethyl 2-[5-fluoro-4-oxo-2-[7H-purin-6-yl(sulfanyl)methyl]quinazolin-3-yl]acetate is the IUPAC name of a molecule. Please give its molecular formula.
user
C18H15FN6O3S
assistant