You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
Please write the molecular formula of the molecule methyl (8S,12R,13S)-8,12-dimethyl-17-nitro-4-propan-2-yl-21-azapentacyclo[12.7.0.02,7.08,13.015,20]henicosa-1(14),2(7),3,5,15(20),16,18-heptaene-12-carboxylate .
user
C27H30N2O4
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