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 5-(2-chlorophenyl)-2-[[1-(2,4-difluorophenyl)ethylamino]methyl]-3H-thieno[2,3-d]pyrimidin-4-one is given. What is its corresponding molecular formula?
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C21H16ClF2N3OS
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