GUI Box doesn't work

Hey,

I got piece of code:

 public class BoostMaister : MonoBehaviour {
 
     void OnGui()
     {
         GUI.Box(new Rect(0, 0, Screen.width, Screen.height), "Olof");
     }
 }

Then I added that script to the "Main camera" component, but the GUI doesn't come on the screen. What the hell???