#include <bits/stdc++.h>
using namespace std;

int main()
{
	int k;
	cin >> k;

	double ans = 0;
	for( int i = 1; i <= k; i++ ) {
		ans += 1.0 / i;
	}
	ans /= k;
	if( k == 0 ) ans = M_PI * M_PI / 6;

	cout << fixed << setprecision(12) << ans << endl;
}