You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
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N-[1-(2-chlorophenyl)pyrazol-4-yl]-2-[2-[(4-fluorophenyl)methyl]-1,3-thiazol-4-yl]acetamide is the IUPAC name of a molecule. Please give its molecular formula.
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C21H16ClFN4OS
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