sum textbox value in windows form

SqlCommand cmq = new SqlCommand("select max(PassNo) as PassNo from dbo.VisitorPass ", objConn1);

                  SqlDataReader drq = cmq.ExecuteReader();
                  if (drq.Read())
                  {
                      int integer;
                      int Qu = 1;
                   txtvpassno.Text = Convert.ToString(drq["PassNo"]);
                   int.TryParse(txtvpassno.Text, out integer);
                   int sum = integer + Qu;
                   txtvpassno.Text=sum;


                      drq.Close();

                  }
                  objConn1.Close();
              }