You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
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For the molecule named 2-[5-[4-(aminomethyl)-1-oxo-3,4,4a,5,6,7,8,8a-octahydro-2H-phthalazin-6-yl]pyridin-3-yl]benzonitrile by IUPAC nomenclature, provide its molecular formula.
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C21H23N5O
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