In the circuit, shown in the figure, the MOSFET is operating in the saturation zone. The characteristics of the MOSFET is given by $I_D=\frac{1}{2}(V_{GS}-1)^2$ $mA$, where $V_{GS}$ is in $V$. If $V_s=+5V$, then the value of $R_s$ in $K\Omega$ is _______________.
