You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
For the molecule named 3-[1-(5-fluoro-2-methoxyphenyl)ethoxy]-5-(5-methylsulfonylpyridin-3-yl)pyridin-2-amine by IUPAC nomenclature, provide its molecular formula.
user
C20H20FN3O4S
assistant