You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
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5-[[5-[2,6-dimethoxy-4-(4-methylpiperazin-1-yl)phenyl]pyrazolidin-3-yl]amino]pyrazine-2-carbonitrile is the IUPAC name of a molecule. Please give its molecular formula.
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C21H28N8O2
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