You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
ethyl 5-[(6-methyl-4-oxo-5-phenyl-3H-thieno[2,3-d]pyrimidin-2-yl)sulfanylmethyl]furan-2-carboxylate The above is the IUPAC name of a molecule. Write its molecular formula.
user
C21H18N2O4S2
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