You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
For the molecule named 1-[4-(4-ethylpiperazin-1-yl)butyl]-2-methyl-3-[[1-(2-methylpropyl)cyclobutyl]methyl]guanidine by IUPAC nomenclature, provide its molecular formula.
user
C21H43N5
assistant