You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
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Translate the chemical IUPAC name 1-[(2-chloro-4-fluorophenyl)methyl]-3-(4-fluorophenyl)-5,6-dimethyl-4aH-thieno[2,3-d]pyrimidin-1-ium-2,4-dione into its molecular formula.
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C21H16ClF2N2O2S+
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