You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
Convert the IUPAC name of a molecule [(1S,3aR,4aR,5R,8aR,8bR)-1-methoxy-4a,8,8,8a-tetramethyl-1,3,3a,4,5,6,7,8b-octahydroindeno[1,2-c]furan-5-yl] 3-methylbut-3-enoate into molecular formula.
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C21H34O4
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