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

class Program
{
    static int NN => int.Parse(ReadLine());
    static int[] NList => ReadLine().Split().Select(int.Parse).ToArray();
    static int[] NMi => ReadLine().Split().Select(c => int.Parse(c) - 1).ToArray();
    static int[][] NMap(int n) => Enumerable.Repeat(0, n).Select(_ => NMi).ToArray();
    public static void Main()
    {
        Solve();
    }
    static void Solve()
    {
        var n = NN;
        var ans = 0.0;
        var d = 0.0001;
        for (var i = 0.0 + d / 2; i <= 1; i += d)
        {
            ans += Math.Sqrt(i * i * i + n * n * n) * d;
        }
        WriteLine(ans);
    }
}