#include <cstdio>
#include <iostream>
#include <sstream>
#include <fstream>
#include <iomanip>
#include <algorithm>
#include <cmath>
#include <string>
#include <vector>
#include <list>
#include <queue>
#include <stack>
#include <set>
#include <map>
#include <bitset>
#include <numeric>
#include <limits>
#include <climits>
#include <cfloat>
#include <functional>
using namespace std;

int main()
{
    vector<double> a(101);
    a[0] = 4;
    a[1] = 3;
    for(int i=2; i<=100; ++i)
        a[i] = (19 * a[i-1] - 12 * a[i-2]) / 4;

    int n;
    cin >> n;
    printf("%.10f\n", a[n]);

    return 0;
}