You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
N-[(4-ethoxyphenyl)methyl]-N-[(1-methylimidazol-2-yl)methyl]-6-azaspiro[2.5]octan-2-amine;hydrochloride is the IUPAC name of a molecule. Please give its molecular formula.
user
C21H31ClN4O
assistant