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