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What is the molecular formula of the molecule identified by ethyl (1R,3R,3aR,6aR)-5-ethyl-1-(2-fluorophenyl)-3-methyl-4,6-dioxo-1,2,3a,6a-tetrahydropyrrolo[3,4-c]pyrrol-2-ium-3-carboxylate ?
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C18H22FN2O4+
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