The values of conductivity of some materials at $298.15 \mathrm{~K}^{-1} ~\text{in} ~\mathrm{Sm}^{-1}$ are $2.1 \times 10^3$,

$1.0 \times 10^{-16}, 1.2 \times 10,3.91,1.5 \times 10^{-2}, 1 \times 10^{-7}, 1.0 \times 10^3$.

The number of conductors among the materials is _____________.