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

#define REP(i, n) for(int i=0; i<(n); i++)

int K;
signed main()
{
    cin >> K;
    double ret = 0;
    int trynum = 1e6;
    REP(i,trynum) {
        int s = 0;
        int cnt = 0;
        while(true) {
            s += 1 + rand() % 6;
            cnt++;
            if (s == K) {
                ret += 1.0 * cnt / trynum;
                break;
            } else if (s > K) {
                s = 0;
            }
        }
    }
    printf("%.14f\n", ret);
    return 0;
}