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 (10aR)-7,8-dimethoxy-2-(2-methylphenyl)-3-sulfanylidene-10,10a-dihydro-5H-imidazo[1,5-b]isoquinolin-1-one is given. What is its corresponding molecular formula?
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C20H20N2O3S
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