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