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)-N,4-dimethyl-2-[methyl-[(2S)-4-methyl-2-[methyl-[(2S)-2-(propanoylamino)propyl]amino]pentanoyl]amino]pentanamide .
user
C21H42N4O3
assistant