You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
(1R,4aS,8aS)-5,5,8a-trimethyl-1-(3-oxobutyl)-1,4,4a,6,7,8-hexahydronaphthalene-2-carboxylic acid The above is the IUPAC name of a molecule. Write its molecular formula.
user
C18H28O3
assistant