You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
N-ethyl-N'-[3-(4-methyl-1,4-diazepan-1-yl)propyl]-1-thia-4-azaspiro[5.5]undecane-4-carboximidamide;hydroiodide is the IUPAC name of a molecule. Please give its molecular formula.
user
C21H42IN5S
assistant