You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
N-[2-[[(4S)-4-(3,4-dichlorophenyl)-1,2,3,4-tetrahydronaphthalen-1-yl]methylsulfanyl]ethyl]formamide is the IUPAC name of a molecule. Please give its molecular formula.
user
C20H21Cl2NOS
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