c# office interop copy slide to another pppt

using PPT = Microsoft.Office.Interop.PowerPoint;

public void Main()
{
    PPT.Application app = new PPT.Application();
    app.Visible = MsoTriState.msoCTrue;
    PPT.Presentation ppt1 = app.Presentations.Open(@"C:\Presentation1.pptx");
    ppt1.Slides[1].Copy();

    PPT.Presentation ppt2 = app.Presentations.Open(@"C:\Presentation2.pptx");
    ppt2.Windows[1].View.GotoSlide(1);

    app.CommandBars.ExecuteMso("PasteSourceFormatting");

}