You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
Convert the IUPAC name of a molecule [(8R,9S,10R,13S,14S,17S)-10,13-dimethyl-3,6-dioxo-2,7,8,9,11,12,14,15,16,17-decahydro-1H-cyclopenta[a]phenanthren-17-yl] acetate into molecular formula.
user
C21H28O4
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