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(Integral(x => (f(x) + (r + R) / 2.0) * (f(x) + (r + R) / 2.0) - ((-f(x) + (r + R) / 2.0) * (-f(x) + (r + R) / 2.0)), 0, (R - r) / 2.0) * 2 * PI * C);

        double f(double x)
        {
            return Sqrt((R - r) / 2.0 * (R - r) / 2.0 - x * x);
        }
    }

    static double Integral(Func<double, double> f, double a, double b, int n = 50000)
    {
        n *= 2;
        var w = (b - a) / n;

        var res = (f(a) + f(b)) * w / 3;
        for (int i = 1; i < n; i++)
        {
            res += f(a + w * i) * ((i & 1) == 0 ? 2 : 4) * w / 3;
        }

        return res;
    }
}