You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
For the molecule named 2-[(1S)-1-[2-(4-methoxyphenoxy)ethylsulfanyl]ethyl]-5-thiophen-2-yl-3H-thieno[2,3-d]pyrimidin-4-one by IUPAC nomenclature, provide its molecular formula.
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C21H20N2O3S3
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