You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
Provide the molecular formula for the IUPAC named substance (8S,9S,10R,13S,14S)-13-ethyl-11-methylidene-2,6,7,8,9,10,12,14,15,16-decahydro-1H-cyclopenta[a]phenanthrene-3,17-dione .
user
C20H26O2
assistant