#include <bits/stdc++.h>
const int MAXN = 5e5 + 10;
const double eps = 1e-8;
const int MOD = 1000000007;
const int INF = 1e9 + 7;
using namespace std;
long long a[105];
long long gcd(long long a, long long b) { return b ? gcd(b, a % b) : a; }
int main() {
  long long fz, fm;
  int n;
  scanf("%d", &n);
  scanf("%lld", &a[0]);
  fz = 1;
  fm = a[0];
  for (int i = 1; i < n; i++) {
    scanf("%lld", &a[i]);
    long long k = gcd(fm, a[i]);
    fz = fz * a[i] / k + fm / k;
    fm = a[i] * fm / k;
  }
  printf("%.9f\n", 1.0 * fm / (1.0 * fz));
  return 0;
}
