iAds scripting problem

I am trying to get an iAd banner in my unity ios game, but when I use this code:

 private ADBannerView banner = null;
 void Start()
 {
     banner = new ADBannerView(ADBannerView.Type.Banner, ADBannerView.Layout.Top);
     ADBannerView.onBannerWasClicked += OnBannerClicked;
     ADBannerView.onBannerWasLoaded  += OnBannerLoaded;
 }
 
 void OnBannerClicked()
 {
     Debug.Log("Clicked!\n");
 }
 
 void OnBannerLoaded()
 {
     Debug.Log("Loaded!\n");
     banner.visible = true;
 }

I get this error message: Assets/scripts/iAds.cs(1,22): error CS0116: A namespace can only contain types and namespace declarations