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 7-[(6-methylpyridin-2-yl)methoxy]-2-pyridin-3-ylsulfonyl-5-thia-2-azaspiro[3.4]octane is given. What is its corresponding molecular formula?
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C18H21N3O3S2
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