You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
Translate the chemical IUPAC name (3R,3'aR,8'aS,8'bS)-5-ethyl-2'-(2-methoxy-5-nitrophenyl)spiro[1H-indole-3,4'-5,6,7,8,8a,8b-hexahydro-3aH-pyrrolo[3,4-a]pyrrolizin-5-ium]-1',2,3'-trione into its molecular formula.
user
C25H25N4O6+
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