#include <iostream>
#include <iomanip>
#include <cassert>
#include <map>
using namespace std;
using ll = long long;
template<class T> inline bool chmax(T& a, const T& b) {if (a<b) {a=b; return true;} return false;}
template<class T> inline bool chmin(T& a, const T& b) {if (b<a) {a=b; return true;} return false;}
const int INTINF = 1000001000;
const int INTMAX = 2147483647;
const ll LLMAX = 9223372036854775807;
const ll LLINF = 1000000000000000000;

int main() {
  ios::sync_with_stdio(0); cin.tie(0); cout.tie(0);
  ll N; cin >> N;
  map<ll,double> memo;

  memo[1] = 0.0;

  auto solve = [&memo] (auto self, ll n) -> double {
    if (memo.contains(n)) return memo.at(n);

    double divsum = 0;
    for (int d=2; d*d <= n; d++) {
      if (n % d == 0) {
        divsum += self(self, d);

        if (d != n/d) {
          divsum += self(self, n/d);
        }
      }
    }

    double ret = double(n) / double(n-1) + divsum / double(n-1);
    memo[n] = ret;
    return ret;
  };
  cout << fixed << setprecision(10);
  cout << solve(solve,N) << endl;
  return 0;
}