You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
7-chloro-1-methyl-3-[(4-pyridazin-4-ylphenyl)methyl]-3,4-dihydro-1,4-benzodiazepine-2,5-dione The above is the IUPAC name of a molecule. Write its molecular formula.
user
C21H17ClN4O2
assistant