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


namespace AtCoder
{
    public class Program
    {
        public static void Main(string[] args)
        {
            var n = int.Parse(ReadLine());
            //var s = Conasole.ReadLine().Split(' ')
            double[] ans = new double[1001];
            ans[0] = 2.07079632677096370230;
            for (int i = 1; i < 1001; i++)
            {
                double j = Math.Sin(i) / i;
                ans[i] = ans[i - 1] - j * j;
            }


            WriteLine(ans[n]);
            Out.Flush();
        }




    }



}