You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
3-(2-chlorophenyl)-N-[(4-methoxyphenyl)methyl]-5-oxo-[1,3]thiazolo[3,2-a]pyrimidine-6-carboxamide is the IUPAC name of a molecule. Please give its molecular formula.
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C21H16ClN3O3S
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