OpenFileDialog opf = new OpenFileDialog();
            opf.Filter = "Файл Excel|*.XLSX;*.XLS";
            opf.ShowDialog();
            string filename = opf.FileName;

            Microsoft.Office.Interop.Excel.Application ExcelApp = new Microsoft.Office.Interop.Excel.Application();
            Microsoft.Office.Interop.Excel._Workbook ExcelWorkBook;
            Microsoft.Office.Interop.Excel.Worksheet ExcelWorkSheet;

            ExcelWorkBook = ExcelApp.Workbooks.Open(filename, 0, true, 5, "", "", true, Microsoft.Office.Interop.Excel.XlPlatform.xlWindows, "t", false,
                false, 0, true, 1, 0);
            ExcelWorkSheet = (Microsoft.Office.Interop.Excel.Worksheet)ExcelWorkBook.Worksheets.get_Item(1);
            ExcelApp.Cells[7,7].Value =1;