You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
N-[(2-methoxyphenyl)methyl]-N-methyl-2,3,3a,4,5,6,7,7a-octahydro-1H-indole-2-carboxamide;hydrochloride is the IUPAC name of a molecule. Please give its molecular formula.
user
C18H27ClN2O2
assistant