How to fix this error when work with Excel 2013 and C# (it work perfect with ".xls")?

Question

I have this code:

        using Excel = Microsoft.Office.Interop.Excel;
        private void GetActiveExcelFile()
       {     
            Excel.Workbook oWB;
            object e;       
                try
                {
                   (Excel.Application)Marshal.GetActiveObject("Excel.Application");
                    e = System.Runtime.InteropServices.Marshal.GetActiveObject("Excel.Application");
                }
                catch (Exception ex)
                {
                    Type type = Type.GetTypeFromProgID("Excel.Application");
                    e = System.Activator.CreateInstance(type);
                };
                Microsoft.Office.Interop.Excel.Application oExcel = (Microsoft.Office.Interop.Excel.Application)e;
                oWB = oExcel.ActiveWorkbook;
                MessageBox.Show(oWB.Worksheets[1].Name);
            }

If my file is ".xls" it work perfect, but if my file is Excel 2013, I got this error: 'object' does not contain a definition for 'Name' and no extension method 'Name' accepting a first argument of type 'object' could be found (are you missing a using directive or an assembly reference?) Hope you can help me. Thanks a lot. Sorry If my English is terrible.