import java.util.*;

public class Main {
    public static void main(String[] args) {
        Scanner s = new Scanner(System.in);
        int n=s.nextInt();
        List<Double> l = new ArrayList<>();
        for (int i = 0; i < n; i++) {
            l.add(s.nextDouble());
        }
        double ans=0;
        for(int i=0;i<n;i++){
            ans+=(1/l.get(i));
        }
        System.out.println(1/ans);
    }
}
/tmp/hf-datasets-cache/medium/datasets/42704881117311-config-parquet-and-info-qiankunmu-Project_CodeNet-896c9d36/hub/datasets--qiankunmu--Project_CodeNet_Python800_and_Java250/snapshots/c899fde44a77ba1cc14973ed3de064e4ff3aadc7/Project_CodeNet_Java250.tar.gz