A projectile is fired from horizontal ground with speed v and projection angle $\theta$. When the acceleration due to gravity is g , the range of the projectile is d . If at the highest point in its trajectory, the projectile enters a different region where the effective acceleration due to gravity is $\mathrm{g}^{\prime}=\frac{\mathrm{g}}{0.81}$, then the new range is $\mathrm{d}^{\prime}=\mathrm{nd}$. The value of $n$ is $\_\_\_\_$ .