#include <bits/stdc++.h>
using namespace std;

double H_approximate(long long n) {
    const double euler_constant = 0.5772156649015328606065121;
    return log(n)+euler_constant+(1.0/2.0)*pow(n, -1.0)-(1.0/12.0)*pow(n, -2.0)+(1.0/120.0)*pow(n, -4.0);
}

int main() {
    constexpr int H_SIZE = 1e7;
    vector<double> H(H_SIZE+1);
    for( int i = 1; i <= H_SIZE; i++ ) {
        H[i] = H[i-1]+pow(i, -1.0);
    }
    long long N;
    cin >> N;
    double ans = 0;
    long long sqrtn = floor(sqrt(N));
    if( N <= 2e6 ) {
        for( int n = 1; n <= N; n++ ) {
            ans += pow(n, -1.0)*H[N/n];
        }
    }else {
        for( int n = 1; n <= sqrtn; n++ ) {
            ans += pow(n, -1.0)*H_approximate(N/n);
        }
        for( int k = 1; k <= sqrtn-1; k++ ) {
            ans += (H_approximate(N/k)-H_approximate(N/(k+1)))*H[k];
        }
    }
    cout << fixed << setprecision(10) << ans << endl;
}