#include "bits/stdc++.h"
using namespace std;
#define FOR(i,j,k) for(int (i)=(j);(i)<(int)(k);++(i))
#define rep(i,j) FOR(i,0,j)
#define each(x,y) for(auto &(x):(y))
#define mp make_pair
#define all(x) (x).begin(),(x).end()
#define debug(x) cout<<#x<<": "<<(x)<<endl
#define smax(x,y) (x)=max((x),(y))
#define smin(x,y) (x)=min((x),(y))
#define MEM(x,y) memset((x),(y),sizeof (x))
#define sz(x) (int)(x).size()
typedef long long ll;
typedef pair<int, int> pii;
typedef vector<int> vi;
typedef vector<ll> vll;

int N;

double calc(double x){
    vector<double> dp(N + 1);
    for(int i = 1; i <= N; ++i){
        for(int j = 1; j <= 6; ++j){
            if(i - j < 0)dp[i] += x;
            else dp[i] += dp[i - j];
        }
        dp[i] = dp[i] / 6 + 1;
    }
    return dp[N];
}

int main(){
    while(cin >> N){
        double L = 0, R = 1e15, M;
        rep(i, 100){
            M = (L + R) / 2;
            (calc(M) >= M ? L : R) = M;
        }
        printf("%0.20f\n", L);
    }
}