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