#include<iostream>
using namespace std;
struct Node
{
    int value;
    Node* next;
    Node()
    {
        value=0;
        next=nullptr;
    }
    Node(int _value,Node* _next)
    {
        this->value=value;
        this->next=_next;
    }
};
class Queue
{
    private:
        Node* head,tail;
        int size;
    public:
        Queue()
        {
            head=nullptr;
            tail=nullptr;
            size=0;
        }
        void pop_front()
        {
            if(head==nullptr&&tail==nullptr) return;
            Node* temp=head->next;
            delete head;
            head=tmp;
            size--;
        }
        void push_back(int value)
        {
            if(head==nullptr&&tail==nullptr)
            {
                Node* temp=new Node(value,nullptr);
                head=temp;
                tail=temp;
                temp=nullptr;
            }
            Node* temp=new Node(value,nullptr);
            tail->next=temp;
            tail=temp;
            temp=nullptr;
            size++;
        }
};
int main () {
return 0;
}