You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
For the molecule named 2-methyl-1-(2-methyl-2-phenylpropyl)-3-[(1-propylpiperidin-4-yl)methyl]guanidine;hydroiodide by IUPAC nomenclature, provide its molecular formula.
user
C21H37IN4
assistant