You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
N,N-dimethyl-6-oxo-7-[(4-propan-2-ylphenyl)methyl]-2,7-diazaspiro[4.5]decane-2-sulfonamide is the IUPAC name of a molecule. Please give its molecular formula.
user
C20H31N3O3S
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