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system
Name the molecular formula for the molecule established as 1-[[3-[3-[3-(difluoromethyl)phenyl]-3-azabicyclo[3.1.0]hexan-6-yl]-1,2,4-oxadiazol-5-yl]methyl]-7-methylpurin-6-one using the IUPAC nomenclature.
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C21H19F2N7O2
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