You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
7-[(3S)-1-(3,5-difluorobenzoyl)pyrrolidin-3-yl]-N,N-dimethylthieno[2,3-b]pyrazine-6-carboxamide is the IUPAC name of a molecule. Please give its molecular formula.
user
C20H18F2N4O2S
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