Invalid casting error when recurring division result is read using OracleDataReader

OracleDataReader is throwing an error when the recursive division(say 1/3) result is returned. No error if the divisions are non-recursive(say 1/2). The error message is "Specified cast is not valid." The code snippet is as follows

string queryString = "Select (1/3) as R from dual";
                using (OracleConnection connection = new OracleConnection(oradb))
                {
                    OracleCommand command = new OracleCommand(queryString, connection);
                    connection.Open();
                    using (OracleDataReader reader = command.ExecuteReader())
                    {
                        ((Oracle.DataAccess.Client.OracleCommand)command).BindByName = true;
                        // Always call Read before accessing data.
                        while (reader.Read())
                        {
                            string s = Convert.ToString(reader[XmlConvert.DecodeName("R")], System.Globalization.CultureInfo.InvariantCulture);
                        }
                    }
                }