#include <iostream>
#include <algorithm>
#include <vector>
#include <queue>
#include <cstdio>
#include <set>
using namespace std;
#define rep(i,n) for(int i=0;i<(n);i++)
const int INF = 1e9;

int k;

double bserach(double mid){//dp[0] = midと仮定
	double dp[300];
	rep(i, 300) dp[i] = 0.0;
	dp[k] = 0.0;
	dp[k + 1] = dp[k + 2] = dp[k + 3] = dp[k + 4] = dp[k + 5] = dp[k + 6] = mid;
	for (int i = k - 1; i >= 0; --i){
		dp[i] = 1.0 + (dp[i + 1] + dp[i + 2] + dp[i + 3] + dp[i + 4] + dp[i + 5] + dp[i + 6]) / 6.0;
	}
	return dp[0];
}

int main(void){
	cin >> k;
	double l = 0.0, r = 100000000.0;
	rep(i, 100){
		double m = (l + r) / 2.0;
		if(bserach(m) >= m){//仮定したdp[0]より大きくなった
			l = m;
		}else{
			r = m;
		}
	}

	printf("%.6f\n", l);
	return  0;
}