#include <iostream>

using namespace std;

struct Node
{
    int data=0;
    Node* next=0;

};

void push( Node *head, int n)
{
    Node *newNode = new Node;
    newNode->data = n;
    newNode->next = 0;
    Node *cur = head;
    while(cur)
    {
        if(cur->next == 0)
        {
            cur->next = newNode;
            return;
        }
        cur = cur->next;
    }
}

int pop(struct Node *head)
{
    int q=0;
    Node *a = head;
    while(a->next)
    {
        a = a->next;
        q++;
    }
    int w = a->data;
    Node *z = head ;
    while(q>1)
    {

        Node* tmpNode;
        tmpNode = head;
        head = tmpNode->next;
        q--;
    }
    delete head->next;
    head->next=0;
    z=head;
    return w ;
}

Node* unshift ( Node *head, int n)
{
    Node *newNode = new Node;
    newNode->data = n;
    newNode->next = head;
    return newNode;
}

int shift (Node *&head)
{
    Node *a;
    int w = head->data;
    a=head->next;
    delete head;
    head=a;
    return w ;
}

int main()
{
    Node* root = new Node;


    root = unshift (root, 10);
    root = unshift (root, 20);
    cout << shift  (root)<< endl << endl;
    cout << shift  (root)<< endl << endl;
    cout << shift  (root)<< endl << endl;

}