import java.util.ArrayList;

abstract class Component {
    private String name;

    Component(String name) {
        this.name = name;
    }

    String getName() {
        return name;
    }

    abstract void accept(Visitor visitor);
}

class Composite extends Component {
    private ArrayList<Component> components = new ArrayList<>();

    Composite(String name) {
        super(name);
    }

    void add(Component component) {
        components.add(component);
    }

    ArrayList<Component> getComponents() {
        return components;
    }

    void accept(Visitor v) {
        v.visit(this);
    }
}

class Element extends Component {
    void accept(Visitor v) {
        v.visit(this);
    }

    Element(String name) {
        super(name);
    }
}


public class Main {
    public static void main(String[] args) {
        Composite root = new Composite("root");
        root.add(new Element("element1"));
        Composite composite1 = new Composite("composite1");
        composite1.add(new Element("element2"));
        composite1.add(new Composite("composite2"));
        composite1.add(new Element("element3"));
        root.add(composite1);
        root.add(new Element("element4"));

        root.accept(new NameVisitor());
    }
}

interface Visitor {
    void visit(Composite composite);
    void visit(Element element);
}

class NameVisitor implements Visitor {
    private int depth = 0;
    private ArrayList<String> names = new ArrayList<>();

    public void visit(Composite composite) {
        names.add(composite.getName());
        ++depth;
        for (Component component: composite.getComponents()) {
            component.accept(this);
        }
        --depth;
        if (depth == 0) {
            display();
        }
    }

    public void visit(Element element) {
        names.add(element.getName());
        display();
    }

    private void display() {
        for (String name: names) {
            System.out.println(name);
        }
    }
}