如何减小get_range()参数中的范围，因为它不接受'-'(-)算子

int nRows = 2;
int nColumns = dt.Rows.Count;
string upperLeftCell = "B2";
int endRowNumber = System.Int32.Parse(upperLeftCell.Substring(1))+ nRows - 1;
char endColumnLetter = System.Convert.ToChar(Convert.ToInt32(upperLeftCell[0]) + nColumns - 1);
string upperRightCell = System.String.Format("{0}{1}",endColumnLetter, System.Int32.Parse(upperLeftCell.Substring(1)));
string lowerRightCell = System.String.Format("{0}{1}",endColumnLetter, endRowNumber);
Excel.Range rg = ws.get_Range(upperLeftCell, lowerRightCell);
for (int i = 1; i <= dt.Rows.Count; i++)
{
   rg[1, i] = dt.Rows[i - 1][0].ToString();      //For Adding Header Text
   rg[2, i] = int.Parse(dt.Rows[i - 1][1].ToString());  //For Adding Datarow Value
}
Excel.Range chartRange = ws.get_Range(upperLeftCell, lowerRightCell);

这是我的代码片段。我需要将lowerRightCell值在我使用它作为参数的两个语句中减少1 !!