#include <string.h>
#include <algorithm>
#include <array>
#include <bitset>
#include <cassert>
#include <cfloat>
#include <climits>
#include <cmath>
#include <complex>
#include <ctime>
#include <deque>
#include <fstream>
#include <functional>
#include <iomanip>
#include <iostream>
#include <iterator>
#include <list>
#include <map>
#include <memory>
#include <queue>
#include <random>
#include <set>
#include <stack>
#include <string>
#include <unordered_map>
#include <unordered_set>
#include <utility>
#include <vector>
using namespace std;

double sum[1001001];

double f(long long l,long long r) {
    double ans = 0;
    if(l <= 1000000) {
        ans += sum[min(r,1000000ll)]-sum[l-1];
    }
    if(r < 1000000) return ans;
    ans += log(r+1);
    ans += (double)(r)/(2*(r+1));
    l = max(1000001ll,l)-1;
    ans -= log(l+1);
    ans -= (double)(l)/(2*(l+1));
    return ans;
}

template<typename T>
vector<pair<T,pair<T,T>>> quotient_range(T N) {
    vector<pair<T,pair<T,T>>>ans;
    T i = 1;
    for(; i*i <= N; i++) {
        ans.push_back({N/i,{i,i}});
    }
    for(; i >= 1; i--) {
        T l = N/(i+1)+1;
        T r = N/i;
        if(l <= r && ans.back().second.first < l) {
            ans.push_back({N/l,{l,r}});
        }
    }
    return ans;
}

int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    long long N;
    cin >> N;
    for(int i = 1; i <= 1000000; i++) {
        sum[i] = sum[i-1]+1.0/i;
    }
    double ans = 0;
    for(auto i:quotient_range(N)) {
        ans += f(1,i.first)*f(i.second.first,i.second.second);
    }
    cout << fixed << setprecision(18) << ans << "\n";
}