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)-butan-2-yl] (6S)-6-(2-chlorophenyl)-3-methyl-4-oxo-1,5,6,7-tetrahydroindole-2-carboxylate .
user
C20H22ClNO3
assistant