You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
Please write the molecular formula of the molecule 2-[[5-[(1R)-1-(4-fluorophenoxy)ethyl]-1,3,4-oxadiazol-2-yl]sulfanylmethyl]-7-methylpyrido[1,2-a]pyrimidin-4-one .
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C20H17FN4O3S
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