You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
Convert the IUPAC name of a molecule ethyl (3R)-1-[2-(4-oxo-2-sulfanylidene-1H-quinazolin-3-yl)acetyl]piperidine-3-carboxylate into molecular formula.
user
C18H21N3O4S
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