You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
Under IUPAC nomenclature, a molecule named 2-(2,5-difluorophenoxy)-1-[(3S)-4-[2-(2,5-difluorophenoxy)acetyl]-3-methylpiperazin-1-yl]ethanone is given. What is its corresponding molecular formula?
user
C21H20F4N2O4
assistant