#include <iostream>
#include <cstdio>
#include <vector>
#include <cmath>
#include <cstring>
#include <numeric>
#include <algorithm>
#include <functional>
#include <array>
#include <map>
#include <queue>
#include <limits.h>
#include <set>
#include <stack>
#define REP(i,n) for(int i = 0; n > i; i++)
#define MOD 1000000007
#define accm(i) ( (i)%2 ? od[((i)-1)/2] : ev[(i)/2])
#define acc(i) ( i%2 ? cpod[(i-1)/2] : cpev[i/2])
using namespace std;
typedef vector<int> Ivec;
typedef pair<int, int> pii;

int main() {
	int n;
	scanf("%d", &n);

	double dp[101] = {};
	dp[0] = 4;
	dp[1] = 3;
	
	for(int i = 2; 100 >= i; i++){
		dp[i] = (dp[i - 1] * 19 - dp[i - 2] * 12) / 4;
	}
	printf("%lf\n", dp[n]);
	return 0;
}