The values of conductivity of some materials at $298.15 \mathrm{~K}^{-1}$ 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 $\_\_\_\_$ .
