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 (3S,3'aR,8'aR,8'bR)-2'-(2-chloro-4-nitrophenyl)-5,7-dimethylspiro[1H-indole-3,4'-3a,6,7,8,8a,8b-hexahydropyrrolo[3,4-a]pyrrolizine]-1',2,3'-trione is given. What is its corresponding molecular formula?
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C24H21ClN4O5
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