import java.util.*;

public class Main 
{
    public static void main(String[] args) throws Exception {
        LinkedList ll = new LinkedList();
        ll.addItem(60);
        ll.addItem(50);
        ll.addItem(40);
        ll.addItem(30);
        ll.addAt(90, 1);
        ll.addAt(1000, 3);
        ll.addAt(0, 3);
        ll.addAt(0, 7);
        ll.display();
    }
}

class LinkedList {

    private class Node {
        int data;
        Node next;
        // Node constructor
        // There are two fields in the node- data and address of next node
        public Node(int data, Node next) {
            this.data = data;
            this.next = next;
        }
    }

    private Node head;
    private Node tail;
    private int size;
    // Linked list constructor
    
     public LinkedList() {
            this.head = null;
            this.tail = null;
            this.size = 0;
        }

    // Function to find the size of linked list
    public int size() {
            return this.size;
        }

    // Function to check whether linked list is empty or not
    public boolean isEmpty() {
        return this.size() == 0;
        }

    // Function to traverse and print the linked list
    public void display() {
        Node temp = head;
        while (temp != null) {
            System.out.print(temp.data + "–>");
            // Set temp to point to the next node
            temp = temp.next;
        }
        System.out.println("END");
    }

    // Function to add a node in linked list
    public void addItem(int item) {
        // Create a temp node which points to head
        Node temp = new Node(item, head);
        // If linked list is empty, temp is the head and tail node both
        if (this.size == 0) {
            this.head = this.tail = temp;
        }
        // else set the head such that it now points to temp node
        else {
            this.head = temp;
        }
        this.size++;
    }

    // Function to add a node at any position in linked list
    public void addAt(int item, int index) throws Exception {
        // Invalid cases
        if (index < 0 || index > this.size) {
            throw new Exception("Index out of bound");
        }
    // Else find the node at (index-1) and change the next pointer
    else {
        // Create a node n pointing to null initially
        Node n = new Node(item, null);
        // Getting node at (index-1)
        int i = 0;
        Node nm1 = head;
        while (i < (index-1)) {
            nm1 = nm1.next;
            i++;
        }
        // Now nm1 is the node at (index-1)
        // Node np1 is the node at (index)
        Node np1 = nm1.next;
        nm1.next = n;
        n.next = np1;   
        this.size++;
        }
    }
}