#include <iostream>
#include <vector>
#include <cstdio>
#include <sstream>
#include <map>
#include <string>
#include <algorithm>
#include <queue>
#include <cmath>

using namespace std;


int main(){
	int k;
	cin >> k;
	vector<double> e(100, 0);
	double a = 1.0/6.0;
	for(int i=0; i<20; i++){
		for(int j=1; j<=6; j++){
			if(i-j<0) break;
			e[i] += e[i-j]*a;
		}
		e[i] += 1;
	}
	printf("%.6f\n", e[k-1]);
	return 0;
}