#include <bits/stdc++.h>
using namespace std;
#define FOR(i,m,n) for(int i=(m);i<(n);++i)
#define REP(i,n) FOR(i,0,n)
using ll = long long;
constexpr int INF = 0x3f3f3f3f;
constexpr long long LINF = 0x3f3f3f3f3f3f3f3fLL;
constexpr double EPS = 1e-8;
constexpr int MOD = 998244353;
// constexpr int MOD = 1000000007;
constexpr int DY4[]{1, 0, -1, 0}, DX4[]{0, -1, 0, 1};
constexpr int DY8[]{1, 1, 0, -1, -1, -1, 0, 1};
constexpr int DX8[]{0, -1, -1, -1, 0, 1, 1, 1};
template <typename T, typename U>
inline bool chmax(T& a, U b) { return a < b ? (a = b, true) : false; }
template <typename T, typename U>
inline bool chmin(T& a, U b) { return a > b ? (a = b, true) : false; }
struct IOSetup {
  IOSetup() {
    std::cin.tie(nullptr);
    std::ios_base::sync_with_stdio(false);
    std::cout << fixed << setprecision(20);
  }
} iosetup;

template <typename T>
std::vector<std::tuple<T, T, T>> enumerate_quotients(const T n) {
  std::vector<std::tuple<T, T, T>> quotients;
  for (T l = 1; l <= n;) {
    const T quotient = n / l, r = n / quotient + 1;
    quotients.emplace_back(l, r, quotient);
    l = r;
  }
  return quotients;
}

int main() {
  constexpr int M = 1000000;
  array<long double, M + 1> memo{};
  FOR(i, 1, M + 1) memo[i] = memo[i - 1] + 1. / i;
  const auto f = [&](const ll r) -> long double {
    return r <= M ? memo[r] : logl(r + 1) + (r + 1.L) / (2LL * (r + 1)) + 0.07721566490153286060651209L;
  };

  ll n; cin >> n;
  long double ans = 0;
  for (const auto& [l, r, q] : enumerate_quotients(n)) {
    ans += (f(r - 1) - f(l - 1)) * f(q);
  }
  cout << ans << '\n';
  return 0;
}