You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
2-butoxy-1-[(3R)-3-[1-(pyridin-4-ylmethyl)imidazol-2-yl]piperidin-1-yl]ethanone is the IUPAC name of a molecule. Please give its molecular formula.
user
C20H28N4O2
assistant