You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
2-[(1S,3R,3aS,6aS)-6'-chloro-5-[2-(3,4-dimethoxyphenyl)ethyl]-7'-methyl-2',4,6-trioxospiro[1,2,3a,6a-tetrahydropyrrolo[3,4-c]pyrrole-3,3'-1H-indole]-1-yl]acetamide The above is the IUPAC name of a molecule. Write its molecular formula.
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C26H27ClN4O6
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