private void button1_Click(object sender, EventArgs e)
        {
            // start excel and turn off msg boxes
            _excelApplication = new XlApplication();
            _excelApplication.DisplayAlerts  = false;
            _excelApplication.ScreenUpdating = false;

            // add a new workbook
            XlWorkbook workBook = _excelApplication.Workbooks.Add();

            // we use the first sheet as summary sheet and remove the 2 last sheets
            XlWorksheet summarySheet = workBook.Worksheets[1];

            workBook.Worksheets[3].Delete();
            workBook.Worksheets[2].Delete();


            // we get the data & perform the report
            _report = new SalesReport(_yearToReport, _monthToReport);
            _report.Proceed();

            // we create named styles for the range.Style property
            CreateStorageAndRankingStyle(workBook, "StorageAndRanking");
            CreateMonthStyle(workBook, "MonthInfos");
            CreateMonthStyle(workBook, "YearTotalInfos");

            // write product sheets
            XlWorksheet productSheet = null;

            foreach (SalesReportProduct itemProduct in _report.Products)
            {
                productSheet = workBook.Worksheets.Add();
                ProceedProductWorksheet(productSheet, itemProduct);
                productSheet.Move(null, workBook.Worksheets[workBook.Worksheets.Count]);
            }

            // write summary sheet
            ProceedSummaryWorksheet(_report, workBook, summarySheet, productSheet);
            summarySheet.Range("$A2").Select();

            // save the book
            string fileExtension = XlConverter.GetDefaultExtension(_excelApplication);
            string workbookFile  = string.Format("{0}\\Example10{1}", Environment.CurrentDirectory, fileExtension);

            workBook.SaveAs(workbookFile);

            // close excel and dispose reference
            _excelApplication.Quit();
            _excelApplication.Dispose();

            FinishDialog fDialog = new FinishDialog("Workbook saved.", workbookFile);

            fDialog.ShowDialog(this);
        }