import java.util.*;
 
public class Main {
    public static void main(String[] args){
    
    Scanner sc = new Scanner(System.in);
    int N = sc.nextInt();
    int[]A = new int[N];
    
    double all = 0;
    for(int i=0; i<N; i++){
    A[i] = sc.nextInt();
    all += (double)1/A[i];
    }
        System.out.println(1/all);
}
}
/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