You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
2-[4-[2-amino-1-(4-fluorophenyl)-2-oxoethyl]piperazin-1-yl]-N-(3-fluorophenyl)propanamide The above is the IUPAC name of a molecule. Write its molecular formula.
user
C21H24F2N4O2
assistant