class Program
    {
        static void Main(string[] args)
        {
            const double pi = Math.PI;
            int calorie = int.Parse(Console.ReadLine());
            string[] size = Console.ReadLine().Split(' ');
            int inNum = int.Parse(size[0]);
            int outNum = int.Parse(size[1]);
            double ans = Math.Acos(calorie*(outNum*outNum - inNum*inNum)*(outNum-inNum)*pi);
            Console.WriteLine(ans );
        }

    }