using System;
using System.Collections.Generic;
using System.Collections;
using System.Linq;
using System.Text;
using sc = Scanner;

class Program
{
    static void Main(string[] args)
    {
        Solve();
#if DEBUG
        System.Console.WriteLine("続行するには何かキーを押してください．．．");
        System.Console.ReadKey();
#endif

    }

    /// <summary>
    /// ここでとく
    /// </summary>
    static void Solve()
    {
        int n = sc.NextInt();
        double[,] mat =
            new double[,] { { 19.0 * 19.0 / 4 - 12.0, -57.0 }, { 19.0, -12.0 } };
        double[] dp = new double[n+10];//oomeni tottoku
        dp[0] = 4.0;
        dp[1] = 3.0;
        for (int i = 2; i + 1 < n + 2; i +=2)
        {
            dp[i + 1] = (mat[0, 0] * dp[i - 1] + mat[0, 1] * dp[i - 2])/4;
            dp[i]     = (mat[1, 0] * dp[i - 1] + mat[1, 1] * dp[i - 2])/4;
        }
        Console.WriteLine(dp[n]);

#if DEBUG
        Console.WriteLine("local check"); // Visual Studioのローカル変数チェック用 MainにいくとSolve内のローカル変数消えちゃう
#endif 

    }

    
}

/// <summary>
/// Java風のスキャナー，自作（某最速の人を参考）
/// </summary>
public static class Scanner
{
    public static string NextString()
    {
        string tmp = "";
        while (true)
        {
            string readData = char.ConvertFromUtf32(Console.Read());
            if (readData == " " || readData == "\n")
                break;
            tmp += readData;
        }
        return tmp;
    }

    public static string[] NextStrArray()
    {
        return Console.ReadLine().Split(' ');
    }

    public static long[] NextLongArray()
    {
        string[] s = NextStrArray();
        long[] a = new long[s.Length];
        for (int i = 0; i < a.Length; i++)
        {
            a[i] = long.Parse(s[i]);
        }
        return a;
    }
    public static int[] NextIntArray()
    {

        string[] s = NextStrArray();
        int[] a = new int[s.Length];
        for (int i = 0; i < a.Length; i++)
        {
            a[i] = int.Parse(s[i]);
        }
        return a;
    }
    public static int NextInt()
    {
        string tmp = "";
        while (true)
        {
            string readData = char.ConvertFromUtf32(Console.Read());
            if (readData == " " || readData == "\n")
                break;
        
            tmp += readData;
        }
        return int.Parse(tmp);
    }
    public static double NextDouble()
    {
        string tmp = "";
        while (true)
        {
            string readData = char.ConvertFromUtf32(Console.Read());
            if (readData == " " || readData == "\n")
                break;
            tmp += readData;
        }
        return double.Parse(tmp);
    }
    public static long NextLong()
    {
        string tmp = "";
        while (true)
        {
            string readData = char.ConvertFromUtf32(Console.Read());
            if (readData == " " || readData == "\n")
                break;
            tmp += readData;
        }
        return long.Parse(tmp);
    }
    public static double[] NextDoubleArray()
    {
        string[] s = NextStrArray();
        double[] a = new double[s.Length];
        for (int i = 0; i < a.Length; i++)
        {
            a[i] = double.Parse(s[i]);
        }
        return a;
    }
}