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What is the molecular formula of the molecule [(4S,9aR)-4-phenyl-3,4,6,7,9,9a-hexahydro-1H-pyrazino[2,1-c][1,4]oxazin-8-yl]-imidazo[1,2-a]pyrimidin-2-ylmethanone ?
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C20H21N5O2
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