#include<bits/stdc++.h>
using namespace std;
using ll = long long;
using ld = long double;
const ld euler_number = 0.577215664901532860606512090082;

ld table[100];

void table_build(){
    table[0] = 0;
    for (int i = 1; i < 100; i++){
        table[i] = table[i-1] + ld(1)/ld(i);
    }
}

ld harmonic_number(ll n){
    if (n < 100) return table[n];
    ld ans = logl(n) + euler_number + ld(1)/ld(2*n) - ld(1)/ld(12*n*n);
    return ans;
}

int main(){
    table_build();
    ll n; cin >> n;
    ld ans = 0;
    ll d = 1;
    while (true){
        ll c = n/d;
        if (c == 0) break;
        ll le = n/(c+1);
        ll ri = n/c;
        ans += harmonic_number(c) * (harmonic_number(ri) - harmonic_number(le));
        d = ri+1;
    }
    cout << fixed << setprecision(20) << ans << endl;
}