You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
Translate the chemical IUPAC name 2-[4-(4-ethoxyphenyl)-3-oxopyrazin-2-yl]sulfanyl-N-[2-(trifluoromethyl)phenyl]acetamide into its molecular formula.
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C21H18F3N3O3S
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