You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
2-[(2-amino-4-methylsulfanylbutanoyl)-(3-methylbutanoyl)amino]-3-(2-ethanethioylphenyl)propanoic acid is the IUPAC name of a molecule. Please give its molecular formula.
user
C21H30N2O4S2
assistant