You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
(4aS,8aR)-1-(2-aminoethyl)-6-(3-methyl-1H-indole-2-carbonyl)-4,4a,5,7,8,8a-hexahydro-3H-1,6-naphthyridin-2-one is the IUPAC name of a molecule. Please give its molecular formula.
user
C20H26N4O2
assistant