You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
Name the molecular formula for the molecule established as 1-(3-chloro-2-fluorophenyl)-3-[3-(6-morpholin-4-ylpyridazin-3-yl)phenyl]urea using the IUPAC nomenclature.
user
C21H19ClFN5O2
assistant