You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
N-(1-cyclopentylbenzimidazol-2-yl)-6,7-dihydro-5H-pyrrolo[1,2-a]imidazole-3-sulfonamide is the IUPAC name of a molecule. Please give its molecular formula.
user
C18H21N5O2S
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