import java.util.*;
class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    int n = sc.nextInt();
    double ans = 0.0;
    double a;

    for(int i=0;i<n;i++) {
      a=sc.nextDouble();
      ans = ans+ 1/a;
    }
    ans = 1/ans;
    System.out.println(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