A hollow cylindrical conductor has length of 3.14 m , while its inner and outer diameters are 4 mm and 8 mm respectively. The resistance of the conductor is $\mathrm{n} \times 10^{-3} \Omega$. If the resistivity of the material is $2.4 \times 10^{-8} \Omega \mathrm{~m}$. The value of n is $\_\_\_\_$