The following diagram shows a Zener diode as a voltage regulator. The Zener diode is rated at \( V_z = 5 \, \text{V} \) and the desired current in load is \( 5 \, \text{mA} \). The unregulated voltage source can supply upto \( 25 \, \text{V} \). Considering the Zener diode can withstand four times of the load current, the value of resistor \( R_s \) (shown in circuit) should be ______ \( \Omega \).
