You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
Translate the chemical IUPAC name (4aR,7aR)-7a-[2,4-difluoro-5-(5-prop-1-ynylpyridin-3-yl)phenyl]-4,4a,5,6-tetrahydrofuro[2,3-d][1,3]thiazin-2-amine into its molecular formula.
user
C20H17F2N3OS
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