How Do I Split A *.Pptx File In Multiple Slide Using Visual Studio 2013 By The Help Of C# ?

OpenFileDialog opObject = new OpenFileDialog();

            opObject.Filter = "Office Documents(*.doc,*.xls,*.pptx)|*.doc;*.xls;*.pptx";

            if (opObject.ShowDialog() == DialogResult.OK)
            {
                string path = opObject.FileName;
                //string pth = Path.GetFileName(path);
                //int num = RetrieveNumberOfSlides(path);
                
                Microsoft.Office.Interop.PowerPoint.Application pptapp = new Microsoft.Office.Interop.PowerPoint.Application();

                Microsoft.Office.Interop.PowerPoint.Presentation ppt1 = pptapp.Presentations.Open(path, Microsoft.Office.Core.MsoTriState.msoFalse,
                Microsoft.Office.Core.MsoTriState.msoFalse, Microsoft.Office.Core.MsoTriState.msoFalse);
                string filename = @"D:\PPT";
                
                int num = ppt1.Slides.Count;

                for (int i = 1; i <=num; i++)
                {
                    string s = i.ToString();
                    string fullpath = filename + s +"ppt";
                    ppt1.Slides[i].Export(fullpath,"ppt");              
                }


            }