You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
[(3R)-3,4-dihydro-1H-isochromen-3-yl]-[(3R)-3-[6-(dimethylamino)pyrazin-2-yl]oxypyrrolidin-1-yl]methanone is the IUPAC name of a molecule. Please give its molecular formula.
user
C20H24N4O3
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