You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
(1'R,2'R,3'R,5'R,7'S,10'S,11'R)-7'-methylspiro[1,3-dioxolane-2,14'-pentacyclo[8.8.0.02,7.03,5.011,16]octadec-16-ene]-6'-one is the IUPAC name of a molecule. Please give its molecular formula.
user
C21H28O3
assistant