You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
(2R)-2-[(3aS,7aS)-5-chloro-1,3-dioxo-3a,4,7,7a-tetrahydroisoindol-2-yl]-N-naphthalen-1-ylpropanamide is the IUPAC name of a molecule. Please give its molecular formula.
user
C21H19ClN2O3
assistant