You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
(2R,3S)-N-[6-(1H-indol-5-yl)pyridazin-3-yl]-2-methyl-1-azabicyclo[2.2.2]octan-3-amine is the IUPAC name of a molecule. Please give its molecular formula.
user
C20H23N5
assistant