You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
4-[(1R,5S)-3-(1-acetylazetidin-3-yl)-9-methoxy-3-azabicyclo[3.3.1]nonan-9-yl]pyridine-2-carboxamide The above is the IUPAC name of a molecule. Write its molecular formula.
user
C20H28N4O3
assistant