You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
What is the molecular formula of the molecule identified by 3,4-dichloro-N-(3,3-dimethyl-4-oxo-5-prop-2-enyl-2H-1,5-benzoxazepin-7-yl)benzamide ?
user
C21H20Cl2N2O3
assistant