You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
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For the molecule named 2-bromo-1-[(8R,9S,10S,13R,14S,17S)-15,15-dihydroxy-10,13-dimethyl-1,2,3,4,5,6,7,8,9,11,12,14,16,17-tetradecahydrocyclopenta[a]phenanthren-17-yl]ethanone by IUPAC nomenclature, provide its molecular formula.
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C21H33BrO3
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