You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
Translate the chemical IUPAC name N-[3-(4-acetylpiperazin-1-yl)-3-oxopropyl]-N-[(4-fluorophenyl)methyl]pyrazine-2-carboxamide into its molecular formula.
user
C21H24FN5O3
assistant