#include <bits/stdc++.h>
using namespace std;
using ll = long long;
int N;
double dp[201];
double test(double d){
    int i,j;
    for(i=1;i<=N;++i){
        dp[i]=0;
        for(j=1;j<=6;++j){
            if(j==i) dp[i]+=0;
            else if(j>i) dp[i]+=d;
            else dp[i]+=dp[i-j];
        }
        dp[i]=dp[i]/6.0+1;
    }
    return dp[N];
}
int main() {
    ios::sync_with_stdio(0);
    cin.tie(0); 
    cin>>N;
    double l=0,r=1e10;
    for(int i_=0;i_<100;++i_){
        auto m=(l+r)/2.;
        if(test(m)>=m) l=m;
        else r=m;
    }
    cout<<fixed<<setprecision(15)<<(l+r)/2.<<endl;
    return 0;
}