#include <cassert>
#include <cmath>
#include <cstdint>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <algorithm>
#include <bitset>
#include <complex>
#include <deque>
#include <functional>
#include <iostream>
#include <limits>
#include <map>
#include <numeric>
#include <queue>
#include <random>
#include <set>
#include <sstream>
#include <string>
#include <unordered_map>
#include <unordered_set>
#include <utility>
#include <vector>

using namespace std;

using Int = long long;

template <class T1, class T2> ostream &operator<<(ostream &os, const pair<T1, T2> &a) { return os << "(" << a.first << ", " << a.second << ")"; };
template <class T> ostream &operator<<(ostream &os, const vector<T> &as) { const int sz = as.size(); os << "["; for (int i = 0; i < sz; ++i) { if (i >= 256) { os << ", ..."; break; } if (i > 0) { os << ", "; } os << as[i]; } return os << "]"; }
template <class T> void pv(T a, T b) { for (T i = a; i != b; ++i) cerr << *i << " "; cerr << endl; }
template <class T> bool chmin(T &t, const T &f) { if (t > f) { t = f; return true; } return false; }
template <class T> bool chmax(T &t, const T &f) { if (t < f) { t = f; return true; } return false; }
#define COLOR(s) ("\x1b[" s "m")


using Double = long double;

constexpr int LIM = 1'000'005;
Double small[LIM];

Double har(Int n) {
  if (n < LIM) return small[n];
  return log((Double)n) + 0.57721566490153286061L + 1.L/2/n - 1.L/12/n/n + 1.L/120/n/n/n/n;
}

int main() {
  for (int i = 1; i < LIM; ++i) {
    small[i] = small[i - 1] + 1.L / i;
  }
  
  Int N;
  for (; ~scanf("%lld", &N); ) {
    Double ans = 0.0;
    for (Int a = 0, b = N; a < N; a = b) {
      const Int k = N / (a + 1);
      b = N / k;
      // (a, b]: k
      ans += (har(b) - har(a)) * har(k);
    }
    printf("%.12Lf\n", ans);
  }
  return 0;
}