#include <bits/stdc++.h>
//#include <atcoder/all>
using namespace std;
//using namespace atcoder;
//using mint = modint1000000007;
//const int mod = 1000000007;
//using mint = modint998244353;
//const int mod = 998244353;
//const int INF = 1e9;
//const long long LINF = 1e18;
#define rep(i, n) for (int i = 0; i < (n); ++i)
#define rep2(i,l,r)for(int i=(l);i<(r);++i)
#define rrep(i, n) for (int i = (n) - 1; i >= 0; --i)
#define rrep2(i,l,r)for(int i=(r) - 1;i>=(l);--i)
#define all(x) (x).begin(),(x).end()
#define allR(x) (x).rbegin(),(x).rend()
#define P pair<int,int>
template<typename A, typename B> inline bool chmax(A & a, const B & b) { if (a < b) { a = b; return true; } return false; }
template<typename A, typename B> inline bool chmin(A & a, const B & b) { if (a > b) { a = b; return true; } return false; }

int main() {
	ios::sync_with_stdio(false);
	cin.tie(nullptr);
	int n; cin >> n;
	vector<vector<int>>v(n + 1);
	rep2(i, 1, n + 1) {
		for (int j = i; j <= n; j += i) {
			v[j].push_back(i);
		}
	}
	vector<double>dp(n + 1);
	rep2(i, 2, n + 1) {
		vector<int>cnt(v[i].size());
		int sz = cnt.size();
		rrep(j, sz) {
			cnt[j] = i / v[i][j];
			rep2(k, j + 1, sz) {
				if (0 == v[i][k] % v[i][j])cnt[j] -= cnt[k];
			}
		}
		rep(j, sz) {
			if (j == sz - 1)break;
			dp[i] += dp[v[i][j]] * cnt[j];
		}
		dp[i] += i;
		dp[i] /= i - 1;
	}
	//rep(i, n + 1) {
	//	cout << i << " " << dp[i] << endl;
	//}
	cout << fixed << setprecision(16) << dp[n] << endl;
	return 0;
}