#include <bits/stdc++.h>
using namespace std;
int euklides(long long a, long long b) {
  while (b != 0) {
    long long c = a % b;
    a = b;
    b = c;
  }
  return a;
}
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  int n;
  cin >> n;
  if (n == 1) {
    long long r;
    cin >> r;
    cout << r;
    return 0;
  }
  long long mianownik = 0;
  long long licznik = 0;
  long long t[n];
  cin >> t[0];
  long long nwd = t[0];
  long long iloczyn = t[0];
  for (int i = 1; i < n; i++) {
    cin >> t[i];
    nwd = euklides(nwd, t[i]);
    iloczyn *= t[i];
  }
  mianownik = iloczyn / nwd;
  for (int i = 0; i < n; i++) {
    int x = mianownik / t[i];
    licznik += x;
  }
  long double w = (long double)mianownik / (long double)licznik;
  printf("%.10Lf", w);
}
