You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
3-[8-methyl-9-[(1R)-1-(5-methylfuran-2-yl)ethyl]purin-2-yl]benzimidazole-5-carbonitrile The above is the IUPAC name of a molecule. Write its molecular formula.
user
C21H17N7O
assistant