You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
2-(2,5-dimethylphenyl)-3-methyl-N-(3-methylbutyl)-1-oxo-4H-pyrazino[1,2-a]indole-3-carboxamide The above is the IUPAC name of a molecule. Write its molecular formula.
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C26H31N3O2
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