You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
2-methyl-N-[1-methyl-2-[2-(2-methylimidazol-1-yl)ethyl]benzimidazol-5-yl]propanamide is the IUPAC name of a molecule. Please give its molecular formula.
user
C18H23N5O
assistant