#include <bits/stdc++.h>
using namespace std;
double E[30];
int K;
double recursive(int x) {
	double e = 0;
	for(int i = 1; i <= 6; i++) {
		if(E[x + i] >= 0) e += E[x + i];
		else e += recursive(x + i);
	}
	e /= 6;
	e += 1;
	E[x] = e;
	return e;
}
int main() {
	cin >> K;
	for(int i = 0; i < 30; i++) {
		E[i] = i >= K ? 0 : -1;
	}
	cout << recursive(0) << endl;
	return 0;
}