Multiple Message box display

I am using slider, in that i am using if condition and message box ,problem is if i move the slider the multiple message box will displaying how to show the only one message box please help me

private void slider_F1_ValueChanged(object sender, RoutedPropertyChangedEventArgs<double> e)
        {

                    p1 = Convert.ToDouble(textBox_F1Yngs.Text);
                    p2 = Convert.ToDouble(textBox_F2Yngs.Text);
                    p3 = Convert.ToDouble(textBox_F3Yngs.Text);
            if(p1 ==0 ||p2 ==0 || p ==0)
            {
                //MessageBox.Show("please select all the values");
                slider_F1.Value = 0;
                slider_F1.Minimum = 0;
            }

            else if(p1>p2 || p2>p3 || p1>p3)
            {



              MessageBox.Show("Check Whether Density of Fluid1 (ρ1) < Density of Fluid2 (ρ2)  <  Density of Fluid3 (ρ3)");
          
  slider_F1.Value = 0;

       
           }

Tags: Silverlight5