SaveAs Dialog Box For Save File in Asp.net Using C#

var fileInfo = new System.IO.FileInfo(filepath);
        Response.ContentType = "application/octet-stream";
        Response.AddHeader("Content-Disposition", String.Format("attachment;filename=\"{0}\"", fileName + ".xlsx"));
        Response.AddHeader("Content-Length", fileInfo.Length.ToString());
        Response.WriteFile(filepath);
        Response.End();