using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace yukicoder
{
    class yc
    {
        static void Main()
        {
            int C = int.Parse(Console.ReadLine());
            string[] str = Console.ReadLine().Split(' ');
            int Rin = int.Parse(str[0]);
            int Rout = int.Parse(str[1]);

            double donut_rad = (Rout - Rin) / 2.0;
            double donut_area = Math.Pow(donut_rad, 2) * Math.PI;
            double dist = donut_rad + Rin;

            Console.WriteLine(donut_area * dist * 2 * Math.PI*C);
        }
    }
}