You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
(E)-N-[[1-(5-chloro-2-methoxybenzoyl)piperidin-3-yl]methyl]-2-cyano-4-methylpent-2-enamide The above is the IUPAC name of a molecule. Write its molecular formula.
user
C21H26ClN3O3
assistant