#include <iostream>
#include <cmath>

using namespace std;
typedef long long ll;
typedef long double ld;
ld h[1000010];
const ld eu = 0.5772156649;
ld H(ll n){
    if(n<=1000000) return h[n];
    return log(n) + eu + (ld)1/(ld)2/(ld)n - (ld)1/(ld)12/(ld)n/(ld)n + (ld)1/(ld)120/(ld)n/(ld)n/(ld)n/(ld)n;
}

int main(){
    cout.precision(20);
    for(int i=1;i<=1000000;i++){
        h[i] = h[i - 1] + (ld)1/(ld)i;
    }
    ll n; cin >> n;
    ld ans = 0;
    for(ll l = 1;l<=n;){
        ll r = n/(n/l);
        if(l>r) break;
        ans += (H(r) - H(l - 1))*H(n/l);
        l = r + 1;
    }
    cout << ans << "\n";
}