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// Node structure
using System;

class Node
{
    public int val;
    public Node next;

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

// Structure to represent queue
class LinkedListQueue
{
    private Node start;
    private Node end;
    private int size;

    public LinkedListQueue()
    {
        this.start = null;
        this.end = null;
        this.size = 0;
    }

    // Method to push an element in the queue
    public void push(int x)
    {
        // Creating a node
        Node element = new Node(x);
        
        // If it is the first element being pushed
        if (this.start == null)
        {
            // Initialize the pointers
            this.start = this.end = element;
        }
        else
        {
            this.end.next = element; // Updating the pointers
            this.end = element; // Updating the end
        }
        
        // Increment size by 1
        this.size++;
    }

    // Method to pop an element from the queue
    public int pop()
    {
        // If the queue is empty
        if (this.start == null)
        {
            return -1; // Pop operation cannot be performed
        }
        
        int value = this.start.val; // Get the front value
        Node temp = this.start; // Store the front temporarily
        this.start = this.start.next; // Update front to next node
        this.size--; // Decrement size
        
        return value; // Return data
    }

    // Method to get the front element in the queue
    public int peek()
    {
        // If the queue is empty
        if (this.start == null)
        {
            return -1; // Front element cannot be accessed
        }
        
        return this.start.val; // Return the front
    }

    // Method to check if the queue is empty
    public bool isEmpty()
    {
        return this.size == 0;
    }
}

public class Program
{
    public static void Main(string[] args)
    {
        // Creating a queue
        LinkedListQueue q = new LinkedListQueue();

        // List of commands
        string[] commands = { "LinkedListQueue", "push", "push", 
                              "peek", "pop", "isEmpty" };
        // List of inputs
        int[][] inputs = { new int[] { }, new int[] { 3 }, new int[] { 7 }, new int[] { }, new int[] { }, new int[] { } };

        for (int i = 0; i < commands.Length; ++i)
        {
            if (commands[i] == "push")
            {
                q.push(inputs[i][0]);
                Console.WriteLine("null");
            }
            else if (commands[i] == "pop")
            {
                Console.WriteLine(q.pop());
            }
            else if (commands[i] == "peek")
            {
                Console.WriteLine(q.peek());
            }
            else if (commands[i] == "isEmpty")
            {
                Console.WriteLine(q.isEmpty() ? "true" : "false");
            }
            else if (commands[i] == "LinkedListQueue")