import java.util.*;

public class Main {
	public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int elements = sc.nextInt();
        int[] value = new int[elements];
        for (int i = 0; i < elements; i++) {
            value[i] = sc.nextInt();
        }
        solve(value);
    }

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

    public static void solve(int[] value){
        double result = 0;
        for(int an : value){
            result += (double) 1/an;
        }
        result = 1/result;
        System.out.println(result);
    }
} Main public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int elements = sc.nextInt();
        int[] value = new int[elements];
        for (int i = 0; i < elements; i++) {
            value[i] = sc.nextInt();
        }
        solve(value);
    } main {
        Scanner sc = new Scanner(System.in);
        int elements = sc.nextInt();
        int[] value = new int[elements];
        for (int i = 0; i < elements; i++) {
            value[i] = sc.nextInt();
        }
        solve(value);
    } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int elements = sc.nextInt(); elements sc.nextInt() sc.nextInt sc int[] value = new int[elements]; value new int[elements] elements for (int i = 0; i < elements; i++) {
            value[i] = sc.nextInt();
        } int i = 0; int i = 0; i 0 i < elements i elements i++ i++ i {
            value[i] = sc.nextInt();
        } {
            value[i] = sc.nextInt();
        } value[i] = sc.nextInt() value[i] value i sc.nextInt() sc.nextInt sc solve(value) solve value String[] args args public static void solve(int[] value){
        double result = 0;
        for(int an : value){
            result += (double) 1/an;
        }
        result = 1/result;
        System.out.println(result);
    } solve {
        double result = 0;
        for(int an : value){
            result += (double) 1/an;
        }
        result = 1/result;
        System.out.println(result);
    } double result = 0; result 0 for(int an : value){
            result += (double) 1/an;
        } int an value {
            result += (double) 1/an;
        } {
            result += (double) 1/an;
        } result += (double) 1/an result (double) 1/an (double) 1 an result = 1/result result 1/result 1 result System.out.println(result) System.out.println System.out System System.out result int[] value value public class Main {
	public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int elements = sc.nextInt();
        int[] value = new int[elements];
        for (int i = 0; i < elements; i++) {
            value[i] = sc.nextInt();
        }
        solve(value);
    }

    public static void solve(int[] value){
        double result = 0;
        for(int an : value){
            result += (double) 1/an;
        }
        result = 1/result;
        System.out.println(result);
    }
} public class Main {
	public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int elements = sc.nextInt();
        int[] value = new int[elements];
        for (int i = 0; i < elements; i++) {
            value[i] = sc.nextInt();
        }
        solve(value);
    }

    public static void solve(int[] value){
        double result = 0;
        for(int an : value){
            result += (double) 1/an;
        }
        result = 1/result;
        System.out.println(result);
    }
} Main
import java.util.*;

public class Main {
	public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int elements = sc.nextInt();
        int[] value = new int[elements];
        for (int i = 0; i < elements; i++) {
            value[i] = sc.nextInt();
        }
        solve(value);
    }

    public static void solve(int[] value){
        double result = 0;
        for(int an : value){
            result += (double) 1/an;
        }
        result = 1/result;
        System.out.println(result);
    }
}