#include <iostream>

using namespace std;

struct ListNode {
    int val;
    ListNode *next;
    ListNode(int x): val(x), next(NULL){}
};


void push(int x, ListNode* head) {
    // 头插法
    ListNode *temp = new ListNode(x);
    temp->next = head->next;
    head->next = temp;
}

void pop(ListNode *head) {

    head->next = head->next->next;
}

int main() {

    ListNode *head = new ListNode(1);

    push(2, head);
    push(3, head);
    push(4, head);

    pop(head);

    while (head) {
        cout << head->val << endl;
        head = head->next;
    }

    return 0;
}