You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
Convert the IUPAC name of a molecule N-[2-methyl-5-[5-(3-nitrosocyclobutyl)-1,2,4-oxadiazol-3-yl]phenyl]imidazo[1,2-a]pyridine-3-carboxamide into molecular formula.
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C21H18N6O3
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