// https://atcoder.jp/contests/abc138/tasks/abc138_b

import java.util.*;
import java.lang.*;
import java.util.stream.*;

public class Main {
    public static void main(String[] args) {
        //コード
        Scanner scanner = new Scanner(System.in);
        Integer x = Integer.parseInt(scanner.next());
        Integer[] arr = new Integer[x];

        for(int i = 0; i < x; i++) {
            arr[i] = Integer.parseInt(scanner.next());
        }

        Double total = 0.0;
        for(int i = 0; i < x; i++) {
            total += ((double)1 / arr[i]);
        }

        System.out.println((double)1 / total);
    }
} import java.util.*; util.* java import java.lang.*; lang.* java import java.util.stream.*; stream.* java.util public class Main {
    public static void main(String[] args) {
        //コード
        Scanner scanner = new Scanner(System.in);
        Integer x = Integer.parseInt(scanner.next());
        Integer[] arr = new Integer[x];

        for(int i = 0; i < x; i++) {
            arr[i] = Integer.parseInt(scanner.next());
        }

        Double total = 0.0;
        for(int i = 0; i < x; i++) {
            total += ((double)1 / arr[i]);
        }

        System.out.println((double)1 / total);
    }
} Main public static void main(String[] args) {
        //コード
        Scanner scanner = new Scanner(System.in);
        Integer x = Integer.parseInt(scanner.next());
        Integer[] arr = new Integer[x];

        for(int i = 0; i < x; i++) {
            arr[i] = Integer.parseInt(scanner.next());
        }

        Double total = 0.0;
        for(int i = 0; i < x; i++) {
            total += ((double)1 / arr[i]);
        }

        System.out.println((double)1 / total);
    } main {
        //コード
        Scanner scanner = new Scanner(System.in);
        Integer x = Integer.parseInt(scanner.next());
        Integer[] arr = new Integer[x];

        for(int i = 0; i < x; i++) {
            arr[i] = Integer.parseInt(scanner.next());
        }

        Double total = 0.0;
        for(int i = 0; i < x; i++) {
            total += ((double)1 / arr[i]);
        }

        System.out.println((double)1 / total);
    } Scanner scanner = new Scanner(System.in); scanner new Scanner(System.in) Integer x = Integer.parseInt(scanner.next()); x Integer.parseInt(scanner.next()) Integer.parseInt Integer scanner.next() scanner.next scanner Integer[] arr = new Integer[x]; arr new Integer[x] x for(int i = 0; i < x; i++) {
            arr[i] = Integer.parseInt(scanner.next());
        } int i = 0; int i = 0; i 0 i < x i x i++ i++ i {
            arr[i] = Integer.parseInt(scanner.next());
        } {
            arr[i] = Integer.parseInt(scanner.next());
        } arr[i] = Integer.parseInt(scanner.next()) arr[i] arr i Integer.parseInt(scanner.next()) Integer.parseInt Integer scanner.next() scanner.next scanner Double total = 0.0; total 0.0 for(int i = 0; i < x; i++) {
            total += ((double)1 / arr[i]);
        } int i = 0; int i = 0; i 0 i < x i x i++ i++ i {
            total += ((double)1 / arr[i]);
        } {
            total += ((double)1 / arr[i]);
        } total += ((double)1 / arr[i]) total ((double)1 / arr[i]) (double)1 arr[i] arr i System.out.println((double)1 / total) System.out.println System.out System System.out (double)1 / total (double)1 total String[] args args public class Main {
    public static void main(String[] args) {
        //コード
        Scanner scanner = new Scanner(System.in);
        Integer x = Integer.parseInt(scanner.next());
        Integer[] arr = new Integer[x];

        for(int i = 0; i < x; i++) {
            arr[i] = Integer.parseInt(scanner.next());
        }

        Double total = 0.0;
        for(int i = 0; i < x; i++) {
            total += ((double)1 / arr[i]);
        }

        System.out.println((double)1 / total);
    }
} public class Main {
    public static void main(String[] args) {
        //コード
        Scanner scanner = new Scanner(System.in);
        Integer x = Integer.parseInt(scanner.next());
        Integer[] arr = new Integer[x];

        for(int i = 0; i < x; i++) {
            arr[i] = Integer.parseInt(scanner.next());
        }

        Double total = 0.0;
        for(int i = 0; i < x; i++) {
            total += ((double)1 / arr[i]);
        }

        System.out.println((double)1 / total);
    }
} Main
// https://atcoder.jp/contests/abc138/tasks/abc138_b

import java.util.*;
import java.lang.*;
import java.util.stream.*;

public class Main {
    public static void main(String[] args) {
        //コード
        Scanner scanner = new Scanner(System.in);
        Integer x = Integer.parseInt(scanner.next());
        Integer[] arr = new Integer[x];

        for(int i = 0; i < x; i++) {
            arr[i] = Integer.parseInt(scanner.next());
        }

        Double total = 0.0;
        for(int i = 0; i < x; i++) {
            total += ((double)1 / arr[i]);
        }

        System.out.println((double)1 / total);
    }
}
