#include<bits/stdc++.h>
using namespace std;
#include<atcoder/all>
using namespace atcoder;
using ll = long long;

int n;
double dpa[202],dpb[202];

void solve(){
	for(int i = n-1;i>=0;i--){
		for(int j = 1;j<=6;j++){
			if(i+j>n){
				dpa[i] += 1/6.0;
			}else{
				dpa[i] += dpa[i+j]/6.0;
				dpb[i] += dpb[i+j]/6.0;
			}
		}
		dpb[i] += 1;
	}
	printf("%.10lf\n",dpb[0]/(1.0-dpa[0]));
}

signed main(){
	cin.tie(nullptr);
	ios::sync_with_stdio(false);
	cin >> n;
	solve();
}