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 2-[3-(4-bromophenyl)-2-oxo-1,4,8-triazaspiro[4.5]dec-3-en-8-yl]-N-(2-fluorophenyl)acetamide ?
user
C21H20BrFN4O2
assistant