You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
2-[[2-[[2-[(2-amino-3-hydroxypropanoyl)amino]-3-methylpentanoyl]amino]-4-methylsulfanylbutanoyl]amino]-4-methylpentanoic acid is the IUPAC name of a molecule. Please give its molecular formula.
user
C20H38N4O6S
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