You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
2-(4-bromophenyl)-3-(2,2-dimethylpropanoyl)-3,10b-dihydro-2H-pyrrolo[2,1-a]isoquinoline-1,1-dicarbonitrile is the IUPAC name of a molecule. Please give its molecular formula.
user
C25H22BrN3O
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