You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
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Under IUPAC nomenclature, a molecule named ethyl (1R,2S,3R,8aS)-6-acetyl-3-carbamoyl-1-cyano-2-(3,4-dichlorophenyl)-3,8a-dihydro-2H-indolizine-1-carboxylate is given. What is its corresponding molecular formula?
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C21H19Cl2N3O4
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