You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
2-methyl-1-[2-(7-methyl-1H-indol-3-yl)ethyl]-3-[2-(6-methylpyridin-3-yl)ethyl]guanidine The above is the IUPAC name of a molecule. Write its molecular formula.
user
C21H27N5
assistant