#include <iostream>

using namespace std;

class Rational {
  public:
    Rational(int n=0, int d=1) : n_(n), d_(d) {}

    int num() const {return n_;}
    int den() const {return d_;}

  private:
    int n_, d_;

    friend ostream& operator<<(ostream&, const Rational&);
};

const Rational operator*(const Rational& lhs, const Rational& rhs) {
  return Rational(lhs.num()*rhs.num(), lhs.den()*rhs.den());
}

ostream& operator<<(ostream& out , const Rational& r) {
  out << r.n_ << "/" << r.d_;
  return out;
}

int main() {
  Rational r1(10);
  Rational r2(3,5);

  cout << "r1 " << r1<< endl;
  cout << "r2 " << r2<< endl;

  Rational r3 = r1 * r2;
  cout << "r3 " << r3<< endl;

  Rational r4 = r1 * 3;
  cout << "r4 " << r4<< endl;

  Rational r5 = 3 * r1;
  // r5 = 3.operator*(r1);  ?? 3 e' in int!
  cout << "r5 " << r5<< endl;

}