You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
2-[2-(dimethylamino)-4-methylpentyl]-1-ethyl-3-[3-(2-oxopyrrolidin-1-yl)propyl]guanidine is the IUPAC name of a molecule. Please give its molecular formula.
user
C18H37N5O
assistant