You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
For the molecule named [(1S,2R,3S,10R,11S,14S,15S)-2,15-dimethyl-4-oxo-14-pentacyclo[8.7.0.02,7.03,7.011,15]heptadec-5-enyl] acetate by IUPAC nomenclature, provide its molecular formula.
user
C21H28O3
assistant