You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
1-[1-(3-chloro-4-fluorophenyl)-2-hydroxyethyl]-4-[2-(propylamino)pyrimidin-4-yl]pyridin-2-one is the IUPAC name of a molecule. Please give its molecular formula.
user
C20H20ClFN4O2
assistant