You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
9-[2-(4-chloro-5-methoxy-1H-indol-3-yl)propanoyl]-7-ethylidene-9-azabicyclo[3.3.1]nonane-3-carbonitrile is the IUPAC name of a molecule. Please give its molecular formula.
user
C23H26ClN3O2
assistant