You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
N-(3,3-dimethyl-4-oxo-5-prop-2-enyl-2H-1,5-benzoxazepin-7-yl)-3-nitrobenzamide is the IUPAC name of a molecule. Please give its molecular formula.
user
C21H21N3O5
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