#pragma GCC target("avx2")
#pragma GCC optimize("Ofast,unroll-loops")
#include <bits/stdc++.h>
#include <atcoder/all>
#define rep(i, n) for (int i = 0; i < n; i++)
#define per(i, n) for (int i = n - 1; i >= 0; i--)
#define ALL(a) a.begin(), a.end()
typedef long double ldouble;
#undef long
#define long long long
#define ll long
#define vec vector
using namespace std;
using mint = atcoder::modint;
ostream &operator<<(ostream &os, mint a)
{
	return os << a.val();
}
template <typename T>
ostream &operator<<(ostream &os, vector<T> &a)
{
	const int n = a.size();
	rep(i, n)
	{
		os << a[i];
		if (i + 1 != n)
			os << " ";
	}
	return os;
}
template <typename T, size_t n>
ostream &operator<<(ostream &os, array<T, n> &a)
{
	rep(i, n) os << a[i] << " \n"[i + 1 == n];
	return os;
}
template <typename T>
istream &operator>>(istream &is, vector<T> &a)
{
	for (T &i : a)
		is >> i;
	return is;
}
template <typename T>
bool chmin(T &x, T y)
{
	if (x > y)
	{
		x = y;
		return true;
	}
	return false;
}
template <typename T>
bool chmax(T &x, T y)
{
	if (x < y)
	{
		x = y;
		return true;
	}
	return false;
}
ldouble harmonic(long n)
{
	if (n <= 1e3)
	{
		ldouble ans = 0;
		for (long i = 1; i <= n; i++)
			ans += 1.0 / i;
		return ans;
	}
	ldouble ans = log(n) + 0.5772156649015328606065120900824024310421593359399235988057672348848677267776646709369470632917467495;
	ans += 1.0 / (2 * n);
	if (n <= 1e8)
		ans -= 1.0 / (12 * n * n);
	if (n <= 1e5)
		ans += 1.0 / (24 * n * n * n);
	return ans;
}
void solve()
{
	long n;
	cin >> n;
	if (n <= 1e8 + 2024)
	{
		ldouble ans = 0;
		for (long i = 1; i <= n; i++)
		{
			for (long j = i; j <= n; j += i)
			{
				ans += 1.0 / j;
			}
		}
		cout << ans << endl;
		return;
	}
	const long nn = (int)sqrt(n);
	ldouble ans = 0;
	for (long i = 1; i <= nn; i++)
	{
		ans += harmonic(n / i) / i;
		ans += harmonic(i) * (harmonic(n / i) - harmonic(n / (i + 1)));
	}
	cout << ans << endl;
}
int main()
{
	// srand((unsigned)time(NULL));
	cin.tie(nullptr);
	ios::sync_with_stdio(false);
	cout << fixed << setprecision(400);
	int t = 1;
	// cin >> t;
	while (t--)
		solve();
	return 0;
}