You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
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(6S)-3-amino-N-[(4-carbamimidoylphenyl)methyl]-1-chloro-8,8-dimethyl-4-oxo-6,7-dihydropyrrolo[1,2-a]pyrazine-6-carboxamide is the IUPAC name of a molecule. Please give its molecular formula.
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C18H21ClN6O2
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