#include <set>
#include <string>
#include <iostream>
#include <numeric>

using namespace std;


// фигура
class Shape {
public:

    string GetColor() const {
        return color_;
    }
    void SetColor(string color) {
        color_ = color;
    }

private:
    string color_ = "black";
};



// прямоугольник
class Rectangle : public Shape {
public:

    Rectangle(double a, double b) : a_(a), b_(b) {}

    double GetArea() {
        return a_ * b_;
    }

private:
    double a_;
    double b_;
};


// треугольник
class Triangle : public Shape {
public:

    Triangle(double a, double b, double c) : a_(a), b_(b), c_(c) {}

    double GetArea() {
        double p = (a_ + b_ + c_) / 2;
        return sqrt(p * (p - a_) * (p - b_) * (p - c_));
    }

private:
    double a_;
    double b_;
    double c_;
};

int main() {
    Rectangle rec(4, 5);
    Triangle tr(3, 4, 3);
    cout << rec.GetArea() << endl;
    cout << tr.GetArea() << endl;
    cout << rec.GetColor() << endl;
    rec.SetColor("white");
    cout << rec.GetColor() << endl;
}