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 (1R,2R,9aR)-1-[2-(furan-3-yl)ethyl]-1,2-dimethyl-2,3,5,8,9,9a-hexahydrobenzo[7]annulene-6-carboxylic acid .
user
C20H26O3
assistant