You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
2-[6-(methylamino)-2-(4-oxo-4-pyridin-4-ylbutyl)-3,4,4a,9b-tetrahydro-1H-pyrido[4,3-b]indol-5-yl]acetaldehyde is the IUPAC name of a molecule. Please give its molecular formula.
user
C23H28N4O2
assistant