You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
Translate the chemical IUPAC name 4-[(9-bromo-6-oxo-7,12-dihydro-5H-indolo[3,2-d][1]benzazepin-3-yl)oxy]butylazanium;chloride into its molecular formula.
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C20H21BrClN3O2
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