using System;
using System.Collections.Generic;
using System.Linq;
using System.Linq.Expressions;
using System.Text;
using System.Threading.Tasks;

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            /*int a, b, c;
            a = int.Parse(Console.ReadLine()); //標準入力
            string[] str = Console.ReadLine().Split(' ');//2つ以上のスペース区切り入力の取得
            b = int.Parse(str[0]);  //数値で受け取りたい場合は変換する
            c = int.Parse(str[1]);
            Console.Write("改行なし a = {0} b = {1} c = {2}", a, b, c);//改行なし出力
            Console.WriteLine("改行あり a = {0} b = {1} c = {2}", a, b, c);//改行付き出力*/

            double cal;
            cal = double.Parse(Console.ReadLine());

            double rin, rout;
            string[] str = Console.ReadLine().Split(' ');
            rin = double.Parse(str[0]);
            rout = double.Parse(str[1]);
            Console.WriteLine(calcal(cal,rin,rout).ToString("0.0000000000"));
        }
        
        static double calcal(double cal,double rin,double rout)
        {
            double r = (rout - rin) / 2;
            double ro = r + rin;
            double r2p = (r * r) * Math.PI;
            double rrp = ro * 2 * Math.PI;

            return (r2p * rrp) * cal;
        }        
    }
}