You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
For the molecule named 3-(2-ethoxy-4-fluorophenoxy)-6-methyl-N-(3-methylsulfonylphenyl)pyridazine-4-carboxamide by IUPAC nomenclature, provide its molecular formula.
user
C21H20FN3O5S
assistant