class Main {
    public static void main (string[] args) {
                Cercle c1 = new Cercle(6.1);
                Cercle c2 = new Cercle(2.7);
                Cercle c3 = new Cercle();

                System.out.printf("%f\n", c1.perimetre());
                System.out.printf("%f\n", c2.perimetre());
                System.out.printf("%f\n", c3.perimetre());
    }
}
class Cercle
{
        public double rayon;

        public Cercle(double r){
                rayon=r;
        }

        public Cercle(){
                rayon=3.45;
        }

        public double perimetre(){
                return 2*Math.PI*rayon;
        }
}

class bob {
    //....
}