#include <bits/stdc++.h>

using namespace std;

#define FOR(i,a,b) for(int i=(a);i<(b);i++)
#define REP(i,n) FOR(i,0,n)
#define ALL(v) (v).begin(),(v).end()

template<typename A, typename B> inline bool chmax(A &a, B b) { if (a<b) { a=b; return 1; } return 0; }
template<typename A, typename B> inline bool chmin(A &a, B b) { if (a>b) { a=b; return 1; } return 0; }

typedef unsigned long long ull;
typedef long long ll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef pair<int, pii> P;

const ll INF = 1ll<<60;
const ll MOD = 1000000007;
const double EPS  = 1e-5;

int K;
double dp[2][201];

int main() {
	cin >> K;
	
	dp[0][0] = 1.0;
	REP(t, 10000) {
		int now = t % 2;
		int next = !now;
		
		memset(dp[next], 0, sizeof(dp[next]));
		
		REP(i, K + 1) FOR(j, 1, 7) {
			if (i + j > K) dp[next][0] += dp[now][i] / 6;
			else dp[next][i + j] += dp[now][i] / 6;
		}
	}
	
	printf("%.15f\n", 1 / dp[1][K] - 1);
	
	return 0;
}