You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
(13S,17S)-13-methyl-3-propyl-6,7,8,9,11,12,14,15,16,17-decahydrocyclopenta[a]phenanthren-17-ol is the IUPAC name of a molecule. Please give its molecular formula.
user
C21H30O
assistant