#include <iostream>
#include <cmath>
#include <cstdio>
#include <algorithm>
#include <string>
#include <vector>
#include <queue>
#include <string.h>
#include <map>
#include <fstream>
#include <functional>
#include <bitset>
#include <iomanip>
#include <stack>
#include <set>
#include <climits>
#define MAX_N 510
#define PI 3.141592653589
#define ESP 1e-20
#define BS 10
#define MOD 1000000007 
#define ZERO 10001
#define YJSNPI 810
#define INF (1LL << 50)
#define ADD(a, b) a = (a + (ll)b) % MOD
#define MUL(a, b) a = (a * (ll)b) % MOD
#define MAX(a, b) a = max(a, b)
#define MIN(a, b) a = min(a, b)

using namespace std;

typedef long long ll;
typedef pair<int, int> pi;

int N;

int main() {
	scanf("%d", &N);
	printf("%.10f\n", 4 * pow(0.75, N));
}