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);
}