You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
(2S)-2-(1-benzylbenzimidazol-2-yl)-2-(5-chloro-1-methyl-3-nitro-6-oxopyridazin-4-yl)acetonitrile The above is the IUPAC name of a molecule. Write its molecular formula.
user
C21H15ClN6O3
assistant