You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
(2S)-2-cyclopentyl-2-[4-(cyclopropanecarbonyl)piperazin-1-yl]-N-(3-fluorophenyl)acetamide is the IUPAC name of a molecule. Please give its molecular formula.
user
C21H28FN3O2
assistant