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-methyl-2-(3-methyl-4-oxophthalazin-1-yl)-N-[2-(2-methylphenoxy)ethyl]acetamide is given. What is its corresponding molecular formula?
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C21H23N3O3
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