using System;

namespace No89_DondonDoughnutsLetsGoWithDawn
{
    internal class Program
    {
        static void Main(string[] args) {
            int c = int.Parse(Console.ReadLine());
            string[] param = Console.ReadLine().Split(' ');
            int rIn = int.Parse(param[0]);
            int rOut = int.Parse(param[1]);

            double s = Math.PI * Math.Pow((rOut - rIn) / 2.0, 2);
            double l = 2 * Math.PI * (rIn + rOut) / 2.0;
            double v = s * l;
            //double v = Math.Pow(Math.PI, 2) * (rIn + rOut) * Math.Pow((rOut - rIn) / 2.0, 2);
            Console.WriteLine(v * c);
        }
    }
}