You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
Translate the chemical IUPAC name benzyl N-[1-[(1R,5S)-6,6-dimethyl-2-bicyclo[3.1.1]hept-2-enyl]but-3-enyl]carbamate into its molecular formula.
user
C21H27NO2
assistant