You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
Translate the chemical IUPAC name 6,6a,7,8,9,11-hexahydropyrrolo[2,1-c][1,4]benzodiazepin-5-yl-[3-(tetrazol-1-yl)phenyl]methanone into its molecular formula.
user
C20H20N6O
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