#include<iostream>
#include<sstream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#include<string>
#include<vector>
#include<cmath>
#include<set>
#include<map>
#include<stack>
#include<queue>
#include<numeric>
#include<functional>
#include<complex>

using namespace std;
#define BET(a,b,c) ((a)<=(b)&&(b)<(c))
#define FOR(i,n) for(int i=0,i##_end=(int(n));i<i##_end;i++)
#define SZ(x) (int)(x.size())
#define ALL(x) (x).begin(),(x).end()
#define MP make_pair
#define FOR_EACH(it,v) for(__typeof(v.begin()) it=v.begin(),it_end=v.end() ; it != it_end ; it++)
typedef vector<int> VI;
typedef vector<VI> VVI;

int main()
{
    int K;
    cin>>K;
    vector<double> a(K+1), b(K+1);
    a[K] = 0, b[K] = 0;
    for(int i=K-1;i>=0;i--){
        for(int j=1;j<=6;j++){
            if(i + j > K){
                a[i]++;
                b[i]++;
            }else {
                a[i] += a[i+j];
                b[i] += b[i+j] + 1.0;
            }
        }
        a[i] /= 6.0;
        b[i] /= 6.0;
    }
    // a * x + b = x
    // x = b / (1 - a)
    double x0 = b[0] / (1.0 - a[0]);
    printf("%.10f\n", x0);
    return 0;
}