You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
(3aS,5aR,7R,9aR,9bS)-7-[(2R)-2-methoxy-2-methylpentyl]-3a-methyl-2,4,5,5a,6,7,8,9,9a,9b-decahydro-1H-cyclopenta[a]naphthalen-3-one The above is the IUPAC name of a molecule. Write its molecular formula.
user
C21H36O2
assistant