A uniform ladder of length 70m and weight W rests against a vertical wall at an angle of ${{45}^{o}}$ with the wall. The coefficient of friction of the ladder with the ground and the wall are $\frac{1}{2}$ and $\frac{1}{3}$ respectively. A man of weight $\frac{W}{2}$ climbs the ladder without slipping. The height in metre to which he can climb is