You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
(3R)-2-[(4-chlorophenyl)methyl]-3-methyl-N-[(1S,2R)-2-methylcyclohexyl]-1-oxo-4H-pyrazino[1,2-a]benzimidazole-3-carboxamide is the IUPAC name of a molecule. Please give its molecular formula.
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C26H29ClN4O2
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