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 (3aR,5S,8aR,9aR)-5,8a-dimethyl-3-methylidene-5,6,7,8,9,9a-hexahydro-3aH-benzo[f][1]benzofuran-2-one .
user
C15H20O2
assistant