You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
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Under IUPAC nomenclature, a molecule named [(8S,9R,13R,14R,17S)-13-methylspiro[7,8,9,11,12,14,15,16-octahydro-6H-cyclopenta[a]phenanthrene-17,2'-oxirane]-3-yl] acetate is given. What is its corresponding molecular formula?
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C21H26O3
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