You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
(1S,4aR,5S,8aS)-5-[(4S)-4,5-dihydroxy-3-methylidenepentyl]-1,4a-dimethyl-6-methylidene-3,4,5,7,8,8a-hexahydro-2H-naphthalene-1-carboxylic acid is the IUPAC name of a molecule. Please give its molecular formula.
user
C20H32O4
assistant