#include <vector>
#include <list>
#include <map>
#include <set>
#include <deque>
#include <stack>
#include <queue>
#include <bitset>
#include <algorithm>
#include <functional>
#include <numeric>
#include <utility>
#include <sstream>
#include <iostream>
#include <iomanip>
#include <cstdio>
#include <cmath>
#include <cstdlib>
#include <cctype>
#include <string>
#include <cstring>
#include <ctime>

using namespace std;

typedef long long ll;
typedef unsigned long long ull;

static const double EPS = 1e-8;
static const double PI = 4.0 * atan(1.0);
static const double PI2 = 8.0 * atan(1.0);

#define REP(i,n)	for(int i=0;i<(int)n;++i)
#define ALL(c)		(c).begin(),(c).end()
#define CLEAR(v)	memset(v,0,sizeof(v))
#define MP(a,b)		make_pair((a),(b))
#define ABS(a)		((a)>0?(a):-(a))
#define FOR(i,s,n)	for(int i=s;i<(int)n;++i)

double memo[30];
int K;

double E(int x) {
	if (x >= K) return 0.0;
	if (memo[x] >= 0.0) return memo[x];
	memo[x] = (E(x + 1) + E(x + 2) + E(x + 3) + E(x + 4) + E(x + 5) + E(x + 6) + 6) / 6.0;
	return memo[x];
}

int main(int argc, char **argv) {
	cin >> K;
	memset(memo, -1, sizeof(memo));
	cout << E(0) << endl;
	return 0;
}