You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
1-[4-[2-[1-(6-chloropyridazin-3-yl)piperidin-4-yl]ethoxy]-3-methylphenyl]-N-ethoxymethanimine is the IUPAC name of a molecule. Please give its molecular formula.
user
C21H27ClN4O2
assistant