using System;
using System.Collections.Generic;
using System.Linq;

class Program
{
    static string InputPattern = "Input3";

    static List<string> GetInputList()
    {
        var WillReturn = new List<string>();

        if (InputPattern == "Input1") {
            WillReturn.Add("0");
            //4.00000000
        }
        else if (InputPattern == "Input2") {
            WillReturn.Add("4");
            //1.265625
        }
        else {
            string wkStr;
            while ((wkStr = Console.ReadLine()) != null) WillReturn.Add(wkStr);
        }
        return WillReturn;
    }

    static void Main()
    {
        List<string> InputList = GetInputList();
        int N = int.Parse(InputList[0]);

        decimal[] AArr = new decimal[100 + 1];
        AArr[0] = 4;
        AArr[1] = 3;

        for (int I = 2; I <= 100; I++) {
            AArr[I] = (19 * AArr[I - 1] - 12 * AArr[I - 2]) / 4;
        }
        Console.WriteLine(AArr[N]);
    }
}