class Cercle {
        private double rayon;
        private static double DEFAULT_RAYON = 1.0;

        void bob(double r) {
                rayon=r;
        }

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

        public Cercle() {
            this(DEFAULT_RAYON);
        }

        public void bob(){
            rayon=3.45;
        }

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

        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());
        }
}