Excel.Range xl = (Excel.Range)worksheet.get_Range("Q2:Q" + lastRowOfTheSheet);
 var all = xl.Rows.Cast<Excel.Range>().Select(x => x.Value2.ToString()).ToList();
 var theRowsSameValue = xl.Rows.Cast<Excel.Range>().Where(y => y.Value2 != ?????????).Select(x => x.Row).ToList();