You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
Translate the chemical IUPAC name 3a-benzyl-9b-hydroxy-3-(2-hydroxyethyl)-5-methyl-2-sulfanylidene-1H-imidazo[4,5-c]quinolin-4-one into its molecular formula.
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C20H21N3O3S
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