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 N-(4-hydroxyphenyl)-4-[(4-oxo-5,6,7,8-tetrahydro-3H-quinazolin-2-yl)sulfanyl]butanamide is given. What is its corresponding molecular formula?
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C18H21N3O3S
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