#include <iostream>

struct Node {
    int value;
    Node *next;
    Node():value(0),next(nullptr) {}
};
class Stack {
    Node *head;
public:
    Stack() : head(nullptr) {}

    void push(int x) {
        Node *tmp = new Node;
        tmp->value = x;
        tmp->next = head;
        head = tmp;
    }

    int top() {
        checker();
        return head->value;
    }

    void pop() {
        checker();
        Node *tmp = head;
        head = head->next;
        delete tmp;
    }

    Stack (const Stack& other):

    {}

    ~Stack() {
        while (head != nullptr) {
            pop();
        }
    }

private:
    void checker()
    {
        if (head==nullptr)
        {
            throw std::runtime_error(" Called on empty list");
        }
    }
};

int main()
{
    Stack s;
    s.top();
}