import java.util.ArrayList; 
import java.util.List;


// Observable interface representing the social media feed
interface Feed {
    void postUpdate(String update);
    void addFollower(Follower follower);
    void notifyFollowers();
}
// Follower interface representing the followers
interface Follower {
    void receiveUpdate(String update);
}


// Concrete observable representing the social media feed
class SocialMediaFeed implements Feed {
    private List<Follower> followers = new ArrayList<>();
    private String update;


    @Override
    public void postUpdate(String update) {
        this.update = update;
        notifyFollowers();
    }


    @Override
    public void addFollower(Follower follower) {
        followers.add(follower);
    }


    @Override
    public void notifyFollowers() {
        for (Follower follower : followers) {
            follower.receiveUpdate(update);
        }
    }
}


// Concrete SocialMediaFollower representing a Follower
class SocialMediaFollower implements Follower {
    private String name;
    public SocialMediaFollower(String name) {
        this.name = name;
    }


    @Override
    public void receiveUpdate(String update) {
        System.out.println(name + " received update: " + update);
    }
}