You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
(3R)-3-imidazol-1-yl-1-[4-(4-methyl-1H-benzimidazol-2-yl)piperidin-1-yl]butan-1-one is the IUPAC name of a molecule. Please give its molecular formula.
user
C20H25N5O
assistant