You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
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Under IUPAC nomenclature, a molecule named 2-[2-(2-methoxyethyl)-5-(3-methoxyphenyl)-4-oxothieno[2,3-d]pyrimidin-3-yl]acetic acid is given. What is its corresponding molecular formula?
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C18H18N2O5S
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