#include <iostream>
using namespace std;
class kruznica {
private:
    double radius;
    const double PI = 3.14159;

public:
    kruznica() {

    }
    kruznica(double _radius) {
        radius = _radius;
    }
    void set_radius(double _radius) {
        radius = _radius;
    }
    double get_radius() {
        return radius;
    }
    double get_PI() const {
        return PI;
    }
    double presmetaj_perimetar() const {
        return 2 * radius * PI;
    }
};

int main() {
    kruznica k(5.6);

    cout << k.get_PI() << endl;
    return 0;
}