You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
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Convert the IUPAC name of a molecule (4R,4aR,7S,7aR,12bS)-9-(hydroxymethoxy)-3-methyl-2,4,4a,7,7a,13-hexahydro-1H-4,12-methanobenzofuro[3,2-e]isoquinolin-7-ol into molecular formula.
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C18H21NO4
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