#include <bits/stdc++.h>
using namespace std;

int dp[223456][3];
bool used[223445][3];
int n, a[312312], b[312312], c[312312];
int mx;
vector <int> v[5];
int mn = 50102031;

long long f = 1, s;
int main() {
   
   cin >> n;
  	long long ggg;
  	cin>> ggg;
  	f = ggg;
  	s = 1;
   for(int i = 1; i <= n - 1; i++){
   long long trr;
   cin >> trr;
   s = trr / __gcd(f, trr) + s * f / __gcd(f, trr);
   f = (f *trr / __gcd(f, trr));
   
   }cout << fixed << setprecision(6) << f * 1./ s;
    //cout << f << ' ' << s;
   }

