You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
(10S)-13-ethyl-10,17-dimethyl-2,3,4,5,6,7,8,9,11,12,14,15,16,17-tetradecahydro-1H-cyclopenta[a]phenanthren-3-ol is the IUPAC name of a molecule. Please give its molecular formula.
user
C21H36O
assistant