You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
ethyl 2-[3-[7,7-difluoro-2-[(2S)-2-methylazetidin-1-yl]-5,6-dihydrocyclopenta[d]pyrimidin-4-yl]-3-azabicyclo[3.1.1]heptan-6-yl]acetate is the IUPAC name of a molecule. Please give its molecular formula.
user
C21H28F2N4O2
assistant