import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.Arrays;
import java.util.Collections;

public class Main {
    public static void main(String args[]) throws IOException {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        int n = Integer.parseInt(br.readLine());
        String[] line = br.readLine().split(" ", 0);
        
        double a = 0, sum = 0;
        for (int i = 0; i < n; i++) {
            a = Double.parseDouble(line[i]);
            sum += 1 / a;
        }
        
        System.out.println(1 / sum);
    }
} import java.io.BufferedReader; BufferedReader java.io import java.io.IOException; IOException java.io import java.io.InputStreamReader; InputStreamReader java.io import java.util.Arrays; Arrays java.util import java.util.Collections; Collections java.util public class Main {
    public static void main(String args[]) throws IOException {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        int n = Integer.parseInt(br.readLine());
        String[] line = br.readLine().split(" ", 0);
        
        double a = 0, sum = 0;
        for (int i = 0; i < n; i++) {
            a = Double.parseDouble(line[i]);
            sum += 1 / a;
        }
        
        System.out.println(1 / sum);
    }
} Main public static void main(String args[]) throws IOException {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        int n = Integer.parseInt(br.readLine());
        String[] line = br.readLine().split(" ", 0);
        
        double a = 0, sum = 0;
        for (int i = 0; i < n; i++) {
            a = Double.parseDouble(line[i]);
            sum += 1 / a;
        }
        
        System.out.println(1 / sum);
    } main {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        int n = Integer.parseInt(br.readLine());
        String[] line = br.readLine().split(" ", 0);
        
        double a = 0, sum = 0;
        for (int i = 0; i < n; i++) {
            a = Double.parseDouble(line[i]);
            sum += 1 / a;
        }
        
        System.out.println(1 / sum);
    } BufferedReader br = new BufferedReader(new InputStreamReader(System.in)); br new BufferedReader(new InputStreamReader(System.in)) int n = Integer.parseInt(br.readLine()); n Integer.parseInt(br.readLine()) Integer.parseInt Integer br.readLine() br.readLine br String[] line = br.readLine().split(" ", 0); line br.readLine().split(" ", 0) br.readLine().split br.readLine() br.readLine br " " 0 double a = 0 a 0 sum = 0; sum 0 for (int i = 0; i < n; i++) {
            a = Double.parseDouble(line[i]);
            sum += 1 / a;
        } int i = 0; int i = 0; i 0 i < n i n i++ i++ i {
            a = Double.parseDouble(line[i]);
            sum += 1 / a;
        } {
            a = Double.parseDouble(line[i]);
            sum += 1 / a;
        } a = Double.parseDouble(line[i]) a Double.parseDouble(line[i]) Double.parseDouble Double line[i] line i sum += 1 / a sum 1 / a 1 a System.out.println(1 / sum) System.out.println System.out System System.out 1 / sum 1 sum String args[] args public class Main {
    public static void main(String args[]) throws IOException {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        int n = Integer.parseInt(br.readLine());
        String[] line = br.readLine().split(" ", 0);
        
        double a = 0, sum = 0;
        for (int i = 0; i < n; i++) {
            a = Double.parseDouble(line[i]);
            sum += 1 / a;
        }
        
        System.out.println(1 / sum);
    }
} public class Main {
    public static void main(String args[]) throws IOException {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        int n = Integer.parseInt(br.readLine());
        String[] line = br.readLine().split(" ", 0);
        
        double a = 0, sum = 0;
        for (int i = 0; i < n; i++) {
            a = Double.parseDouble(line[i]);
            sum += 1 / a;
        }
        
        System.out.println(1 / sum);
    }
} Main
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.Arrays;
import java.util.Collections;

public class Main {
    public static void main(String args[]) throws IOException {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        int n = Integer.parseInt(br.readLine());
        String[] line = br.readLine().split(" ", 0);
        
        double a = 0, sum = 0;
        for (int i = 0; i < n; i++) {
            a = Double.parseDouble(line[i]);
            sum += 1 / a;
        }
        
        System.out.println(1 / sum);
    }
}