import java.io.BufferedReader;
import java.util.ArrayList;
import java.io.File;
import java.io.FileReader;
import java.io.FileNotFoundException;
import java.io.IOException;

class Node {
    public int value;
    public Node next;
    public Node prev;
}

public class List {
    //Fill in your code in here and the empty procedures
    private int N = 0;    // number of elements on list
    private Node pre;     // sentinel before first item
    private Node post;    // sentinel after last item

    public List(){
        pre = new Node();
        post = new Node();
    }







    //This function should create a new empty list
    public static List init() {
        return new List();
    }

    //This function should insert the value v in the list between the elemts with index i and index i-1
    /*
     * HEAD->FIRST = newNode

newNode->PREV = NULL

newNode->NEXT = NULL

increment(HEAD->LENGTH)
     */
    public static void insert(List l, int i, int v) {
        Node tmp = new Node();
        tmp.value = v;
        Node go = l.pre.next;

        if(l.N == 0) {
            tmp.next = l.post;
            l.pre.next = tmp;
            l.N++;
        } else {
            for(int iter = 0; iter < i-1; iter++) {
                go = go.next;
            }
            tmp.prev = go;
            tmp.next = go.next;
            tmp.prev.next = tmp;
            go.next = tmp;
            l.N = l.N+1;

        }

    }

    //This function should return the number of elemts in the list
    public static int size(List l) {
        return l.N;
    }

    //This function should return the value of the element at index i in the list
    public static int get(List l, int i) {
        if(l == null){
            System.out.println("nope. nothing there.");
        } else {
            Node tmp = l.pre;
            for(int iter = 0; iter < l.N; iter++) {
                tmp = tmp.next;
            }
            return tmp.value;
        }

        return -1;
    }

    //This function should return the value of the element and als remove the element at index i in the list
    public static int remove(List l, int i) {
        i++;
        Node go = l.pre;
        int value = 0;
        for(int iter = 0; iter < i; iter++) {
            value = go.value;
            go = go.next;
        }

        go.prev.next = go.next;
        go.next.prev = go.prev;
        l.N = l.N - 1;

        return value;
    }