#include <bits/stdc++.h>
using namespace std;
unsigned euclidean_gcd(unsigned a, unsigned b) {
  if (a < b) return euclidean_gcd(b, a);
  unsigned r;
  while ((r = a % b)) {
    a = b;
    b = r;
  }
  return b;
}
unsigned euclidean_lcm(unsigned a, unsigned b) {
  unsigned g;
  g = euclidean_gcd(a, b);
  return a * b / g;
}
int main() {
  long long n = 0;
  double mother, child = 0;
  cin >> n;
  vector<double> a(n);
  vector<double> b(n);
  for (long long i = 0; i < n; i++) {
    cin >> a[i];
    b[i] = a[i];
  }
  for (long long j = 1; j < n; j++) {
    a[j] = euclidean_lcm(a[j], a[j - 1]);
    mother = a[j];
  }
  for (int k = 0; k < n; k++) {
    child += mother / b[k];
  }
  cout << setprecision(12) << mother / child << endl;
  return 0;
}
