import java.util.*;

interface LibraryVisitor {
    (1);
    (2);
    void printSum();
}

class LibrarySumPrintVisitor implements LibraryVisitor { // 打印总页数
    private int sum = 0;
    public void visit(Book p_book) {
        sum = sum + p_book.getNumberOfPages();
    }
    public void visit(Article p_article) {
        sum = sum + p_article.getNumberOfPages();
    }
    public void printSum() {
        System.out.println("SUM = " + sum);
    }
}

interface LibraryItemInterface {
    (3);
}

class Article implements LibraryItemInterface {
    private String m_title; // 论文名
    private String m_author; // 论文作者
    private int  m_start_page;
    private int  m_end_page;
    public Article(String p_author, String p_title, int p_start_page, int p_end_page) {
        m_title = p_title;
        m_author = p_author;
        m_start_page = p_start_page;
        m_end_page = p_end_page;        
    }
    public int getNumberOfPages() {
        return m_end_page - m_start_page;
    }
    public void accept(LibraryVisitor visitor) {
        (4);
    }
}

class Book implements LibraryItemInterface {
    private String m_title; // 书名
    private String m_author; // 书作者
    private int m_pages; // 页教
    public Book(String p_author, String p_title,int p_ pages) {
        m_title = p_title;
        m_author = p_author;
        m_pages = p_pages;
    }
    public int getNumberOfPages() {
        return m_pages; 
    }
    public void accept(LibraryVisitor visitor) {
        (5);
    }
}