You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
2-[2-[5-(furan-2-yl)-4-methyl-3,6-dihydro-2H-pyridin-1-yl]-2-oxoethyl]-3H-isoindol-1-one is the IUPAC name of a molecule. Please give its molecular formula.
user
C20H20N2O3
assistant