You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
Name the molecular formula for the molecule established as 1-[6-[(4-bromo-2-chlorophenyl)methyl]-7-fluoro-3-methylbenzimidazol-5-yl]-2-but-3-enoxyethanone using the IUPAC nomenclature.
user
C21H19BrClFN2O2
assistant