You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
1-[2-(2,5-difluorophenyl)ethyl]-2-methyl-3-[2-(6-methylpyridin-3-yl)ethyl]guanidine The above is the IUPAC name of a molecule. Write its molecular formula.
user
C18H22F2N4
assistant