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

namespace Yukicoder
{
    class Program
    {
        static void Main(string[] args)
        {
            var c = int.Parse(Console.ReadLine());
            var line = Console.ReadLine().Split(' ').Select(int.Parse).ToArray();
            var rin = line[0];
            var rout = line[1];
            var mean = (rin + rout)/2d;
            var largeS = Math.PI * (rout - mean) * (rout - mean);
            var v = 2*Math.PI*mean*largeS;
            Console.WriteLine(v * c);
        }
    }
}