You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
2-[3-(4-chlorophenyl)-4-oxoquinazolin-2-yl]sulfanyl-N-(1,1-dioxothiolan-3-yl)-N-methylacetamide is the IUPAC name of a molecule. Please give its molecular formula.
user
C21H20ClN3O4S2
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