You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
Provide the molecular formula for the IUPAC named substance (2S,3aR,7aS)-1-[2-oxo-2-(3-phenylpropylamino)ethyl]-2,3,3a,4,5,6,7,7a-octahydroindole-2-carboxylic acid .
user
C20H28N2O3
assistant