You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
N-[3-(azepan-1-yl)-3-oxo-1-pyridin-3-ylprop-1-en-2-yl]-3-bromobenzamide is the IUPAC name of a molecule. Please give its molecular formula.
user
C21H22BrN3O2
assistant