You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
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For the molecule named 7-[4-(3-ethyl-3-azabicyclo[3.1.0]hexan-1-yl)phenyl]-6,8-dihydro-5H-[1,2,4]triazolo[4,3-a]pyrazine by IUPAC nomenclature, provide its molecular formula.
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C18H23N5
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