private static string GetCellsSumFormula(int cell1Row, int cell1Col, int cell2Row, int cell2Col)
        {
            string cell1Name  = NameConverter.ConvertCellIndexToName(cell1Row, cell1Col);
            string cell2Name  = NameConverter.ConvertCellIndexToName(cell2Row, cell2Col);
            string sumFormula = string.Format("={0}+{1}", cell1Name, cell2Name);

            return(sumFormula);
        }