You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
For the molecule named 3-(3-chloro-8-methylsulfanylbenzo[b][1]benzothiepin-6-yl)-N,N-dimethylprop-2-yn-1-amine by IUPAC nomenclature, provide its molecular formula.
user
C20H18ClNS2
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