You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
Convert the IUPAC name of a molecule (10S,13S,14R,17S)-17-acetyl-10,13-dimethyl-2,4,7,12,14,15,16,17-octahydro-1H-cyclopenta[a]phenanthrene-3,11-dione into molecular formula.
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C21H26O3
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