You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
Translate the chemical IUPAC name 6-[[5-(3,5-difluorophenyl)-1H-pyrazol-4-yl]methyl]-2-methylsulfanyl-7,8-dihydro-5H-pyrido[4,3-d]pyrimidine into its molecular formula.
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C18H17F2N5S
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