#include<iostream>
using namespace std;
int main(){
	double e[30] = { 0 };
	int k;
	cin >> k;
	while (k){
		k--;
		e[k] = (e[k + 1] + e[k + 2] + e[k + 3] + e[k + 4] + e[k + 5] + e[k + 6]) / 6.0 + 1.0;
	}
	cout << e[0] << endl;

	return 0;
}