Problem when inserting data into a database

I have some data that I want to insert in my BD, but the problem is that they are not inserted.

Table creation in BD:

    public class DB extends SQLiteOpenHelper{

    String tabla ="CREATE TABLE Datos (Id INTEGER PRIMARY KEY AUTOINCREMENT, N text, P4 text, P5 text)";

    public DB(Context context, String name, SQLiteDatabase.CursorFactory factory, int version) {
        super(context, name, factory, version);
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        db.execSQL(tabla);
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int versionAnt, int versionNva) {
        //Se elimina la versión anterior de la tabla
        db.execSQL("DROP TABLE IF EXISTS Datos");

        //Se crea la nueva versión de la tabla
        db.execSQL(tabla);
    }
}

In this code, long i equals -1:

EditText preg5 = (EditText) findViewById(R.id.precinco);
    EditText preg4 = (EditText) findViewById(R.id.precuatro);
    EditText nom = (EditText) findViewById(R.id.nombre);
    String nombre = nom.getText().toString();
    //String curso = cur.getSelectedItem().toString();
    String cinco = preg5.getText().toString();
    String cuatro = preg4.getText().toString();
    RadioGroup gruporadio = (RadioGroup) findViewById(R.id.Grupo1);
    RadioGroup gruporadio2 = (RadioGroup) findViewById(R.id.Grupo2);
    RadioGroup gruporadio3 = (RadioGroup) findViewById(R.id.Grupo3);
    //Spinner cur = (Spinner) findViewById(R.id.spinnerp);
    DB baseHelper = new DB(this, "DEMODB", null, 1);
    SQLiteDatabase db = baseHelper.getWritableDatabase();
    if(db != null){
        ContentValues registronuevo = new ContentValues();
        registronuevo.put("N", nombre);
        registronuevo.put("P4", cuatro);
        registronuevo.put("P5", cinco);
        long i = db.insert("Datos", null, registronuevo);
        if (gruporadio.getCheckedRadioButtonId() == -1 || gruporadio2.getCheckedRadioButtonId() == -1 || gruporadio3.getCheckedRadioButtonId() == -1) {
            Toast.makeText(this, "¡No marcaste ninguna respuesta!", Toast.LENGTH_LONG).show();
        }

        else if (nombre.matches("") || cinco.matches("") || cuatro.matches("")) {
            Toast.makeText(this, "¡Dejaste campos vacíos!", Toast.LENGTH_LONG).show();
        }

        else if (i>0){
            Intent pas = new Intent(encuesta.this, MainActivity.class);
            startActivity(pas);
            Toast.makeText(this, "¡Encuesta enviada!", Toast.LENGTH_LONG).show();
        }

        else{
            Toast.makeText(this, "Ocurrió un error, intenta más tarde", Toast.LENGTH_LONG).show();
        }

What can I do to ensure that the data is inserted and that long i is not equal to -1, but is greater than 0?

Thanks in advance.

EDITED: For what it's worth, this is the activity where the inserted data should be displayed:

public void cargar() {

    DB baseHelper = new DB(this, "DEMODB", null, 1);
    SQLiteDatabase db = baseHelper.getReadableDatabase();
    if (db != null) {
        Cursor c = db.rawQuery("select * from Datos", null);
        int cantidad = c.getCount();
        int i = 0;
        String[] arreglo = new String[cantidad];
        if(c.moveToFirst()){
            do{
                String linea = c.getInt(0)+" "+ c.getString(1)+" "+ c.getString(3)+" "+ c.getString(4);
                arreglo[i] = linea;
                i++;

            }while (c.moveToNext());
        }
        ArrayAdapter<String>adapter = new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, arreglo);
        ListView lista = (ListView) findViewById(R.id.lista);
        lista.setAdapter(adapter);
    }
}