#include <iostream>
#include <cstdio>
#include <vector>
#include <algorithm>
#include <utility>

using namespace std;

vector<double> e(26, -1);

double dfs(int x) {
	if (e[x] != -1) {
		return e[x];
	}

	e[x] = 1.0 * (dfs(x+1) + dfs(x+2) + dfs(x+3) + dfs(x+4) + dfs(x+5) + dfs(x+6)) / 6 + 1;
	return e[x];
}

int main() {
	int k;

	cin >> k;
	for (int i = k; i < e.size(); i++) {
		e[i] = 0;
	}
	double ans = dfs(0);
	printf("%.6f\n", ans);
	return 0;
}