You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
1-[1-[3-(3-methyl-8-azabicyclo[3.2.1]octan-8-yl)propyl]indol-3-yl]ethanone is the IUPAC name of a molecule. Please give its molecular formula.
user
C21H28N2O
assistant