#include <iostream>
#include <iomanip> //<<setprecision(12), or <<fixed
#include <algorithm>
#include <functional>
#include <map>
#include <vector>
#include <queue>
#include <cmath>
#include <set>
 
using namespace std;

using ll=long long;
using ull=unsigned long long;
using pll=pair<ll,ll>;

int main()
{
    ll N;
    cin>>N;
    
    vector<double> dpa(N+6+1,0), dpb(N+6+1,0);
    for(ll i=N+1; i<=N+6; i++)
    {
        dpa[i]=1;
    }
    
    for(ll i=N-1; i>=0; i--)
    {
        dpb[i]+=1;
        for(ll k=i+1; k<=i+6; k++)
        {
            dpa[i]+=dpa[k]/6;
            dpb[i]+=dpb[k]/6;
        }
    }
    
    double res=dpb[0]/(1-dpa[0]);
    cout<<fixed<<setprecision(15)<<res<<endl;
    
    // Fear misreading.
    return 0;
}