import java.util.Scanner;

class Node {
    int data;
    Node next;

    public Node(int data) {
        this.data = data;
        this.next = null;
    }
}

class SinglyLinkedList {
    private Node head;

    public void display() {
        Node temp = head;
        while (temp != null) {
            System.out.print(temp.data + " -> ");
            temp = temp.next;
        }
        System.out.println("NULL");
    }

    public void insertAtPosition(int data, int position) {
        Node newNode = new Node(data);
        if (position == 0) {
            newNode.next = head;
            head = newNode;
            return;
        }
        
        Node temp = head;
        for (int i = 0; temp != null && i < position - 1; i++) {
            temp = temp.next;
        }
        
        if (temp == null) {
            System.out.println("Position out of range");
            return;
        }
        
        newNode.next = temp.next;
        temp.next = newNode;
    }

    public void deleteAtPosition(int position) {
        if (head == null) {
            System.out.println("List is empty");
            return;
        }
        
        if (position == 0) {
            head = head.next;
            return;
        }
        
        Node temp = head;
        for (int i = 0; temp != null && i < position - 1; i++) {
            temp = temp.next;
        }
        
        if (temp == null || temp.next == null) {
            System.out.println("Position out of range");
            return;
        }
        
        temp.next = temp.next.next;
    }
}

public class LinkedListDemo {
    public static void main(String[] args) {
        SinglyLinkedList list = new SinglyLinkedList();
        Scanner scanner = new Scanner(System.in);
        
        while (true) {
            System.out.println("\n1. Insert at position\n2. Delete from position\n3. Display\n4. Exit");
            System.out.print("Enter choice: ");
            int choice = scanner.nextInt();
            
            switch (choice) {
                case 1:
                    System.out.print("Enter data: ");
                    int data = scanner.nextInt();
                    System.out.print("Enter position: ");
                    int pos = scanner.nextInt();
                    list.insertAtPosition(data, pos);
                    break;
                case 2:
                    System.out.print("Enter position to delete: ");
                    pos = scanner.nextInt();
                    list.deleteAtPosition(pos);
                    break;
                case 3:
                    list.display();
                    break;
                case 4:
                    scanner.close();
                    return;
                default:
                    System.out.println("Invalid choice");
            }
        }
    }
}