#include <iostream>
#include <string>
#include <algorithm>
#include <vector>
#include <stack>
#include <queue>
#include <list>
#include <set>
#include <map>
#include <numeric>
#include <regex>
#include <tuple>
#include <iomanip>
#include <cmath>
using namespace std;

typedef long long ll;
typedef pair<int, int> P;
#define MOD 1000000007 // 10^9 + 7
#define INF 1000000000 // 10^9
#define LLINF 1LL<<60

double A[109];

int main() {
	cin.tie(0);
	ios::sync_with_stdio(false);

	int N; cin >> N;
	for (int i = 0; i <= N; i++) A[i] = 0;
	A[0] = 4; A[1] = 3;
	for (int i = 2; i <= N; i++) {
		A[i] = (19 * A[i - 1] - 12 * A[i - 2]) / 4;
	}

	//for (int i = 0; i <= N; i++) cout << i << " : " << A[i] << endl;
	cout << setprecision(15) << A[N] << endl;

	return 0;
}