#include<bits/stdc++.h>
using namespace std;

//#define int long long

typedef long long ll;
typedef pair<int,int>pint;
typedef vector<int>vint;
typedef vector<pint>vpint;
#define pb push_back
#define mp make_pair
#define fi first
#define se second
#define ln <<endl
#define all(v) (v).begin(),(v).end()
#define rep(i,n) for(int i=0;i<(n);i++)
#define reps(i,f,n) for(int i=(f);i<(n);i++)
#define each(it,v) for(__typeof((v).begin()) it=(v).begin();it!=(v).end();it++)
template<class T,class U>void chmin(T &t,U f){if(t>f)t=f;}
template<class T,class U>void chmax(T &t,U f){if(t<f)t=f;}

int K;

double dp[222];

bool C(double x){
    for(int i=1;i<=K;i++){
        dp[i]=0;
        for(int j=1;j<=6;j++){
            if(j>i)dp[i]+=x;
            else dp[i]+=dp[i-j];
        }
        dp[i]=1+dp[i]/6.0;
    }

    return dp[K]<=x;
}

signed main(){
    scanf("%d",&K);
    double lb=0,ub=1000000;
    rep(i,100){
        double mid=(ub+lb)/2;
        if(C(mid))ub=mid;
        else lb=mid;
    }

    printf("%.20f\n",ub);
    return 0;
}