An infinite slope is made up of cohesionless soil with seepage parallel to and up to the sloping surface. The angle of slope is $30^{\circ}$ with respect to horizontal ground surface. The unit weights of the saturated soil and water are $20 \mathrm{kN} / \mathrm{m}^{3}$ and $10 \mathrm{kN} / \mathrm{m}^{3}$, respectively.
The minimum angle of shearing resistance of the soil (in degrees) for the critically stable condition of the slope is $\_\_\_\_\_\_\_$ (rounded off to the nearest integer).