private static void ReadExcel(string path)
        {

            IWorkbook workbook;
            ISheet _sheet;

            string fileExt = Path.GetExtension(path);

            using (var file = new FileStream(path, FileMode.Open, FileAccess.Read))
            {
                if (fileExt == ".xls")
                {
                    workbook = new HSSFWorkbook(file);
                }
                else
                {
                    workbook = new XSSFWorkbook(file);
                }
                
            }

            _sheet = workbook.GetSheetAt(0);
            _sheet.GetRow(0).GetCell(0).SetCellValue("1");


            using (var fs = new FileStream(path, FileMode.Create, FileAccess.Write))
            {
                workbook.Write(fs);
            }
        }