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

namespace YukiCoder
{
    class Program
    {
        static void Main(string[] args)
        {
            var na = double.Parse(Console.ReadLine());
            var va = Console.ReadLine().Split().Select(double.Parse).ToArray();
            var Rp = va[1] + va[0];
            var Rm = va[1] - va[0];
            var nn = Rm * Rm * Rp * Math.PI * Math.PI * na / 4;
            Console.WriteLine(nn);
            Console.ReadLine();
        }
    }
}