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

int main(){
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);

    int K; cin >> K;
    vector<double> P(K+1);
    P.at(0) = 1;
    double answer = 0;
    for(int i=0; i<K; i++){
        answer += P.at(i);
        for(int k=1; k<=6; k++) if(i+k <= K) P.at(i+k) += P.at(i)*0.166666666;
    }
    answer *= 1/P.at(K);
    cout << fixed << setprecision(20) << answer << endl;
}