You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
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1-[(4-chloro-1-methylpyrrol-2-yl)methyl]-1,2-dimethyl-3-[[4-(2-oxopyrrolidin-1-yl)phenyl]methyl]guanidine is the IUPAC name of a molecule. Please give its molecular formula.
user
C20H26ClN5O
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