You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
Translate the chemical IUPAC name (2S)-2-amino-3-methyl-N-[2-oxo-2-[[1-oxo-1-(propylamino)propan-2-yl]amino]ethyl]butanamide into its molecular formula.
user
C13H26N4O3
assistant