#include <functional>
#include <iostream>
using namespace std;

void f1(std::function<void()> callback) {
  std::cout << "Hello!" << endl;
  callback();
  std::cout << "Bye!" << endl;
}

int main() {
    f1([] {
        std::cout << "Kimchi!" << endl;
    });
    return 0;
}