You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
N-[2-[4-[(2R,6S)-4-azatricyclo[5.2.2.02,6]undecane-4-carbonyl]phenoxy]ethyl]acetamide is the IUPAC name of a molecule. Please give its molecular formula.
user
C21H28N2O3
assistant