#include <atcoder/all>
#include <bits/stdc++.h>
using ll = long long;
using ull = unsigned long long;
#define rep(i, n) for(int i = 0; i < (int)(n); i++)
#define REP(i, m, n) for(int i = (int)(m); i < (int)(n); i++)
using namespace std;
using namespace atcoder;
using mint = modint998244353;
const int inf = 1000000007;
const ll longinf = 1ll << 60;

int main() {
    ios::sync_with_stdio(false);
    cin.tie(0);
    cout.tie(0);
    ll n;
    cin >> n;
    vector<long double> sum(1000001);
    REP(i, 1, 1000001) {
        sum[i] = sum[i - 1] + 1.0 / i;
    }
    auto calc = [&](ll x) {
        if(x <= 1000000)
            return sum[x];
        else
            return log((long double)x) + 0.5772156649015;
    };
    long double ans = 0;
    REP(i, 1, 1000001) {
        if(i > n / i) {
            break;
        }
        ans += calc(i) * (calc(n / i) - calc(n / (i + 1)));
        // cout << i << " " << cnt << endl;
    }
    REP(i, 1, 1000001) {
        if(i >= n / i) {
            break;
        }
        ans += calc(n / i) / i;
        // cout << i << " " << endl;
    }
    cout << fixed << setprecision(15) << ans << endl;
    return 0;
}