double jump script

hy guys im really blocked , i'm using the default thris person controller from unity , and i want this script to include a double jump , help me please , im begging u people :(

 function ApplyJumping ()
 {
     // Prevent jumping too fast after each other
     if (lastJumpTime + jumpRepeatTime > Time.time)
         return;
 
     if (IsGrounded()) {
         // Jump
         // - Only when pressing the button down
         // - With a timeout so you can press the button slightly before landing        
         if (canJump && Time.time < lastJumpButtonTime + jumpTimeout) {
             verticalSpeed = CalculateJumpVerticalSpeed (jumpHeight);
             SendMessage("DidJump", SendMessageOptions.DontRequireReceiver);
         }
     }
 }