#include<iostream>
#include<string>
#include<iomanip>
#include<cmath>
#include<vector>
#include<algorithm>
#include<utility>

using namespace std;

#define int long long
#define endl "\n"

constexpr long long INF = (long long)1e18;
constexpr long long MOD = 1'000'000'007; 

struct fast_io {
	fast_io(){
		std::cin.tie(nullptr);
		std::ios::sync_with_stdio(false);
	};
} fio;

signed main(){
	cout<<fixed<<setprecision(20);
	
	long double ans = 0;
	int k;
    
	cin>>k;
    
    if(k == 0) {
        cout<<acos(-1) * acos(-1)/6<<endl;
        return 0;
    }
    
    for(int i = 1; i <= k; i++){
        ans += (long double)1/i;
    }
    
    ans /= k;
    
    cout<<ans<<endl;
    
	return 0;
}