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 (Z)-4-[7-bromo-6-chloro-5-(2,6-difluorophenyl)-2-methylidene-3H-1,4-benzodiazepin-1-yl]but-3-en-2-one ?
user
C20H14BrClF2N2O
assistant