You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
ethyl 4-(4-bromo-5-methylthiophen-2-yl)-2-methyl-5-oxo-4,6,7,8-tetrahydro-1H-quinoline-3-carboxylate is the IUPAC name of a molecule. Please give its molecular formula.
user
C18H20BrNO3S
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