You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
2-(6-bromo-1-oxospiro[3H-isoquinoline-4,1'-cyclopropane]-2-yl)-N-[(3S)-1-(oxetan-3-yl)piperidin-3-yl]acetamide The above is the IUPAC name of a molecule. Write its molecular formula.
user
C21H26BrN3O3
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