#include <iostream>

    void countdown(int n) {
        std::cout << "countdown(" << n << ") entry\n";
        if (n == 0)
            countdown(n + 1);
        std::cout << "countdown(" << n << ") exit\n";
    }

    int main() {
        std::cout << "main entry\n";
        countdown(0);
        std::cout << "main exit\n";
    }