#include <bits/stdc++.h>
using namespace std;
int main() {
  int N;
  cin >> N ;
  double X=0;
  for(double i = 1; i < N; i++){
    X +=  N/i;
  }
  cout << std::fixed << std::setprecision(12) << X << endl;
}
#include <bits/stdc++.h>
using namespace std;
const int maxn = 2e6;
typedef long long ll;
template<class T> T read()
{
	T f = 1, k = 0;
	char c = getchar();
	while (c < '0' || c > '9')
	{
		if (c == '-')
			f = -1;
		c = getchar();
	}
	while (c >= '0' && c <= '9')
	{
		k = k * 10 + c - '0';
		c = getchar();
	}
	return f * k;
}

double n, ans;
vector<int> v[maxn];
int main()
{
	n = read<double>();
	for (double i = 1; i < n; i++)
	{
		ans += 1.000000 / i;
	}
	ans *= n;
	printf("%lf\n", ans);
}
