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