You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
ethyl 5-hydroxy-4-oxo-1,3-diphenyl-2-sulfanylidenethieno[2,3-d]pyrimidine-6-carboxylate is the IUPAC name of a molecule. Please give its molecular formula.
user
C21H16N2O4S2
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