You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
3-[(3R,3aR,6S,7S,9bR)-3a,6,9b-trimethyl-3-[(1E)-1-(4-methyl-5-oxofuran-2-ylidene)propan-2-yl]-7-prop-1-en-2-yl-1,2,3,4,5,5a,7,8-octahydrocyclopenta[a]naphthalen-6-yl]propanoic acid is the IUPAC name of a molecule. Please give its molecular formula.
user
C30H42O4
assistant