You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
N-[(1R)-1-(4-bromophenyl)ethyl]-2-[(2S)-3-oxo-4H-1,4-benzoxazin-2-yl]acetamide is the IUPAC name of a molecule. Please give its molecular formula.
user
C18H17BrN2O3
assistant