Мне нужно имя листа вместо имени листа по умолчанию

// creating Excel Application
Microsoft.Office.Interop.Excel._Application app = new Microsoft.Office.Interop.Excel.Application();
// creating new WorkBook within Excel application
Microsoft.Office.Interop.Excel._Workbook workbook = app.Workbooks.Add(Type.Missing);
// creating new Excelsheet in workbook
//Microsoft.Office.Interop.Excel._Worksheet worksheet = null;
Worksheet worksheet = null;
// see the excel sheet behind the program
app.Visible = false;
// get the reference of first sheet. By default its name is Sheet1.
// store its reference to worksheet
worksheet = (Worksheet)workbook.Sheets["Sheet1"];
//worksheet = (Worksheet)workbook.Worksheets.get_Item(0);
worksheet = (Worksheet)workbook.ActiveSheet;
// changing the name of active sheet
int m = 1;
int totcolumns = ds.Tables[0].Columns.Count;  //get column numbers
//worksheet.Name = "Sheet1";
ReportsProgress(35, "adding data into new excel file");
#region adding column header
DataRow ch = ds.Tables[0].Rows[0];

for (int j = 1; j < totcolumns + 1; j++) //Line added by raghu30082013
{
    //worksheet.Cells[m, j] = "F" + j.ToString();
    worksheet.Cells[m, j] = ch[j-1].ToString();     //Added by Siva (Same column header as source excel) 05 April 2016
}
#endregion

//worksheet = (Worksheet)workbook.Sheets["Sheet1"];
worksheet = (Worksheet)workbook.Worksheets.get_Item(0);