#include<bits/stdc++.h>
using namespace std;
using LL = long long;
using ULL = unsigned long long;
#define rep(i,n) for(int i=0; i<(n); i++)

int main() {

	cout << fixed << setprecision(10);

	LL K; cin >> K;
	if (K == 0) { cout << (acos(-1.) * acos(-1.) / 6.) << endl; return 0; }

	double ans = 0.;
	for(LL i = 1; i <= K; i++) {
		ans += 1 / double(K * i);
	}
	cout << ans << endl;
	return 0;
}