You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
2-cyclohexyl-N-[2-(2-pyridin-4-ylimidazo[4,5-b]pyridin-3-yl)ethyl]acetamide The above is the IUPAC name of a molecule. Write its molecular formula.
user
C21H25N5O
assistant