You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
(5S)-5-[(4-chlorophenyl)methyl]-3-(2,4-dimethylphenyl)-4,5-dihydro-1H-pyridazin-6-one is the IUPAC name of a molecule. Please give its molecular formula.
user
C19H19ClN2O
assistant