Simplest pointer-based C++ stack definition

SimplestStack.cpp

#include <iostream>
#include <stdexcept>

template <typename T>
class Stack
{
public:
    void push(T elem)
    {
        auto n = new Node;
        n->elem = elem;
        n->prev = last;
        last = n;
        _size++;
    }
    T& peek()
    {
        if(empty())
            throw std::underflow_error("Cannot peek empty stack!");
        return last->elem;
    }

    T pop()
    {
        if(empty())
            throw std::underflow_error("Cannot pop empty stack!");


        auto n = this->last;
        this->last = n->prev;
        auto el = n->elem;

        _size--;
        delete n;

        return el;
    }
    const int size() const { return _size; }
    const bool empty() const { return _size == 0; }
private:

    struct Node
    {
        T elem;
        Node* prev;
    };

    Node* last = nullptr;
    int _size = 0;
};

int main() {
    Stack<int> stack;
    std::cout << "Stack is empty " << stack.empty() << std::endl;

    stack.push(1);
    stack.push(2);

    std::cout << "Stack size " << stack.size() << std::endl;
    std::cout << "Pop: " << stack.pop() << ", peek " << stack.peek() << ", pop: " << stack.pop() << std::endl;
    std::cout << "Size: " << stack.size() << std::endl;

    return 0;
}