#include <cstdio>
#include <iostream>
#include <sstream>
#include <fstream>
#include <iomanip>
#include <algorithm>
#include <cmath>
#include <string>
#include <vector>
#include <list>
#include <queue>
#include <stack>
#include <set>
#include <map>
#include <bitset>
#include <numeric>
#include <limits>
#include <climits>
#include <cfloat>
#include <functional>
using namespace std;

int main()
{
    int k;
    cin >> k;

    vector<pair<double, double> > dp(k+1);
    for(int i=1; i<=k; ++i){
        for(int j=i-6; j<=i-1; ++j){
            if(j < 0){
                dp[i].first += 1.0 / 6.0;
                dp[i].second += 1.0 / 6.0;
            }
            else{
                dp[i].first += (dp[j].first + 1.0) / 6.0;
                dp[i].second += dp[j].second / 6.0;
            }
        }
    }

    double ret = dp[k].first / (1 - dp[k].second);
    printf("%.10f\n", ret);

    return 0;
}