A steel rod has a radius of 20 mm and a length of 2.0 m. A force of 62.8 kN stretches it along its length. Young's modulus of steel is $2.0 \times 10^{11}\mathrm{~N~m}^{-2}$. The longitudinal strain produced in the wire is $\_\_\_\_$ $\times 10^{-5}$.