using System;
using System.Collections.Generic;
using System.Linq;
using static System.Console;
using static System.Math;

class Program
{
    static void Main()
    {
        var C = int.Parse(ReadLine());
        var rR=ReadLine().Split().Select(int.Parse).ToArray();
        var r =rR[0];
        var R =rR[1];
        WriteLine((R-r)/2.0*(R-r)/2.0*PI*(r+(R-r)/2.0)*2*PI*C);
    }
}