#include <bits/stdc++.h>
using namespace std;
const int maxd = 1e5 + 10;
int n, arr[maxd];
__int128 gcd(__int128 x, __int128 y) {
  if (!y) return x;
  return gcd(y, x % y);
}
int main() {
  scanf("%d", &n);
  for (int i = 1; i <= n; i++) scanf("%d", &arr[i]);
  __int128 x = 1, y = arr[1];
  for (int i = 2; i <= n; i++) {
    __int128 g = gcd(arr[i], y);
    x = arr[i] / g * x + y / g;
    y = y * arr[i] / g;
    g = gcd(x, y);
    y /= g, x /= g;
  }
  printf("%.10lf", 1.0 * y / x);
  return 0;
}
