You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
For the molecule named 3-[2-(1,5-dimethylbenzimidazol-2-yl)ethylamino]-5,6-dimethylpyridazine-4-carbonitrile by IUPAC nomenclature, provide its molecular formula.
user
C18H20N6
assistant