#include <bits/stdc++.h>
using namespace std;
#define GET_MACRO(a, b, c, NAME, ...) NAME
#define rep(...) GET_MACRO(__VA_ARGS__, rep3, rep2)(__VA_ARGS__)
#define rep2(i, a) rep3 (i, 0, a)
#define rep3(i, a, b) for (int i = (a); i < (b); i++)
#define repr(...) GET_MACRO(__VA_ARGS__, repr3, repr2)(__VA_ARGS__)
#define repr2(i, a) repr3 (i, 0, a)
#define repr3(i, a, b) for (int i = (b) - 1; i >= (a); i--)
template<class T1, class T2> inline bool chmin(T1 &a, T2 b) { return b < a && (a = b, true); }
template<class T1, class T2> inline bool chmax(T1 &a, T2 b) { return a < b && (a = b, true); }
using ll = long long;

struct XorShift {
    unsigned z;
    XorShift() : z((unsigned)time(NULL)) {}
    XorShift(int seed) : z(z) {}
    unsigned next() {
        z ^= z << 13;
        z ^= z >> 17;
        z ^= z << 5;
        return z;
    }
    int next_int(int a, int b) {
        return next() % (b - a) + a;
    }
    double next_double() {
        return next() / (double)(1ll << 32);
    }
} rng;

int main() {
	int k;
	cin >> k;
	vector<int> dist(22);
	rep (i, 101010) {
		int s = 0;
		int num = 0;
		while (s < k) {
			s += rng.next_int(1, 7);
			num++;
		}
		dist[num]++;
	}
	double ans = 0;
	rep (i, 22) ans += dist[i] * i;
	ans /= 101010;
	printf("%.20f\n", ans);
	return 0;
}