Eight halides are heated separately in 80% aqueous ethanol at $50^{\circ }\mathrm{C}$ with no added strong nucleophile: 2-chloro-2-methylpropane, chlorodiphenylmethane, bromobenzene, 3-bromo-3-methylpentane, bromoethene, iodomethane, 1-bromo-1-methylcyclohexane and 1-bromobutane. For how many of them is substitution by the unimolecular SN1 pathway the dominant route? Give the answer as an integer.

Numerical answer type, tolerance 0.5.