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 2-(7-ethenyl-9-hydroxy-1,4a,7-trimethyl-8-oxo-2,3,4,5,6,9,10,10a-octahydrophenanthren-1-yl)acetic acid is given. What is its corresponding molecular formula?
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C21H30O4
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