You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
For the molecule named (5R,8S,9R,10S,13S,14R,15S)-10,13-dimethyl-17-oxo-1,2,3,4,5,6,7,8,9,11,12,14,15,16-tetradecahydrocyclopenta[a]phenanthrene-15-carbonitrile by IUPAC nomenclature, provide its molecular formula.
user
C20H29NO
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