Press back button to show Ad and Quit?

I have been trying to implement a code that enables the user to press the back button to quit, but before he can, an ad shows up.

Press back button > Ad shows > press back button again > quit.
Here is the code that works that enables the user to press the back button,

if (interstitial.IsLoaded ()) {
if (Input.GetKeyDown (KeyCode.Escape)) {
interstitial.Show ();
}
}

I tried multiple codes to try to get the user to see the ad and then quit, but none works.

Maybe something like…

if (interstitial.IsLoaded ()) 
{ 
     if (Input.GetKeyDown (KeyCode.Escape)) 
     { 
         if (interstitial.isShowing)
         {
             interstitial.Hide(); 
         }
         else
         {
             interstitial.Show ();
         }
     }
}

Also don’t put everything on one line like that, it makes it impossible to read. Even such a simple statement like this is difficult.

Sorry about that,

I can get my interstitial to show just fine when I press the escape button.

But after the user presses the escape button AGAIN, I want to exit the program.

First press= show ad
Second press= quit

the App “Super Androix” has this, I’m trying to figure out how they accomplished it…