You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
10,13-dimethylspiro[1,2,4,7,8,9,11,12,14,15,16,17-dodecahydrocyclopenta[a]phenanthrene-3,2'-1,3-dioxolane]-17-ol The above is the IUPAC name of a molecule. Write its molecular formula.
user
C21H32O3
assistant