You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
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Convert the IUPAC name of a molecule 2-chloro-7-ethyl-12,13-dimethoxy-9,10-dihydro-7H-isoquinolino[2,1-d][1,4]benzodiazepin-6-one into molecular formula.
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C21H21ClN2O3
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