You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
For the molecule named 2-ethyl-1-[3-(2-propylimidazo[4,5-b]pyridin-3-yl)pyrrolidin-1-yl]butan-1-one by IUPAC nomenclature, provide its molecular formula.
user
C19H28N4O
assistant