You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
1-ethyl-3-[2-(2-methoxyphenyl)ethyl]-2-[4-(2-oxopyridin-1-yl)butyl]guanidine;hydroiodide is the IUPAC name of a molecule. Please give its molecular formula.
user
C21H31IN4O2
assistant