#include <iostream>
typedef long long ll;
const int MAXN = 1e7 + 5;
using namespace std;
double f[MAXN];
int N, phi[MAXN];
double dfs(int a) {
	if (f[a] || a == 1) return f[a];
	for (int i = 1; i < a; ++i) {
		if (a % i == 0) {
			f[a] += phi[a / i] * (dfs(i) + 1.0);
		}
	}
	f[a] = (f[a] + 1.0) / (a - 1.0);
	return f[a];
}
int main() {
	ios::sync_with_stdio(false);
	cin.tie(0);
	cin >> N;
	f[1] = 0;
	for (int i = 1; i <= N; ++i) phi[i] = i;
	for (int i = 2; i <= N; ++i) {
		if (phi[i] == i) {
			phi[i]--;
			for (int j = i + i; j <= N; j += i) phi[j] -= phi[j] / i;
		}
	}
	cout << dfs(N) << endl;
	return 0;
}