#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;

unsigned xor128(){
    static unsigned x=123456789,y=362436069,z=521288629,w=88675123;
    unsigned t;
    t=(x^(x<<11));x=y;y=z;z=w; return( w=(w^(w>>19))^(t^(t>>8)) );
}

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

    const int T = 5000000;
    int cnt = 0;
    for(int i=0; i<T; ++i){
        int sum = 0;
        while(sum < k){
            sum += xor128() % 6 + 1;
            ++ cnt;
        }
    }

    double ret = cnt / (double) T;
    cout.setf(ios_base::fixed, ios_base::floatfield);
    cout << setprecision(10) << ret << endl;

    return 0;
}