#include <bits/stdc++.h>
#define rep(i, a) for (int i = 0; i < (a); i++)
#define rep2(i, a, b) for (int i = (a); i < (b); i++)
#define repr(i, a) for (int i = (a) - 1; i >= 0; i--)
#define repr2(i, a, b) for (int i = (b) - 1; i >= (a); i--)
using namespace std;
typedef long long ll;
const ll inf = 1e9;
const ll mod = 573;

typedef long double ld;
ld dp[2020];

int main() {
	int N;
	cin >> N;

	dp[0] = 4;
	dp[1] = 3;

	rep2 (i, 2, 2020) {
		dp[i] = 19.0 / 4 * dp[i - 1] - 3.0 * dp[i - 2];
	}

	double ans = dp[N];

	printf("%.20f\n", ans);

	return 0;
}