You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
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Can you give the molecular formula of the molecule (3R,3'aR,8'aR,8'bR)-5-chloro-7-methyl-2'-phenylspiro[1H-indole-3,4'-3a,6,7,8,8a,8b-hexahydropyrrolo[3,4-a]pyrrolizine]-1',2,3'-trione ?
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C23H20ClN3O3
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