import java.util.Scanner;

public class Main {
    public static void main(String[] args){
        new Main().run();
    }

    private void run() {
        Scanner scanner = new Scanner(System.in);
        int N = scanner.nextInt();
        int[] A = new int[N];
        int[] B = new int[N];
        int sum = 0;
        A[0] = scanner.nextInt();
        int l = A[0];

        for(int i = 1; i < N; i ++) {
            A[i] = scanner.nextInt();
            l = lcm(l, A[i]);
        }
        for(int i = 0; i < N; i ++) {
           B[i] = l / A[i];
           sum += B[i];
        }

        System.out.println((double)l/sum);
    }

    static int lcm (int a, int b) {
        int temp;
        long c = a;
        c *= b;
        while((temp = a%b)!=0) {
            a = b;
            b = temp;
        }
        return (int)(c/b);
    }

} import java.util.Scanner; Scanner java.util public class Main {
    public static void main(String[] args){
        new Main().run();
    }

    private void run() {
        Scanner scanner = new Scanner(System.in);
        int N = scanner.nextInt();
        int[] A = new int[N];
        int[] B = new int[N];
        int sum = 0;
        A[0] = scanner.nextInt();
        int l = A[0];

        for(int i = 1; i < N; i ++) {
            A[i] = scanner.nextInt();
            l = lcm(l, A[i]);
        }
        for(int i = 0; i < N; i ++) {
           B[i] = l / A[i];
           sum += B[i];
        }

        System.out.println((double)l/sum);
    }

    static int lcm (int a, int b) {
        int temp;
        long c = a;
        c *= b;
        while((temp = a%b)!=0) {
            a = b;
            b = temp;
        }
        return (int)(c/b);
    }

} Main public static void main(String[] args){
        new Main().run();
    } main {
        new Main().run();
    } new Main().run() new Main().run new Main() String[] args args private void run() {
        Scanner scanner = new Scanner(System.in);
        int N = scanner.nextInt();
        int[] A = new int[N];
        int[] B = new int[N];
        int sum = 0;
        A[0] = scanner.nextInt();
        int l = A[0];

        for(int i = 1; i < N; i ++) {
            A[i] = scanner.nextInt();
            l = lcm(l, A[i]);
        }
        for(int i = 0; i < N; i ++) {
           B[i] = l / A[i];
           sum += B[i];
        }

        System.out.println((double)l/sum);
    } run {
        Scanner scanner = new Scanner(System.in);
        int N = scanner.nextInt();
        int[] A = new int[N];
        int[] B = new int[N];
        int sum = 0;
        A[0] = scanner.nextInt();
        int l = A[0];

        for(int i = 1; i < N; i ++) {
            A[i] = scanner.nextInt();
            l = lcm(l, A[i]);
        }
        for(int i = 0; i < N; i ++) {
           B[i] = l / A[i];
           sum += B[i];
        }

        System.out.println((double)l/sum);
    } Scanner scanner = new Scanner(System.in); scanner new Scanner(System.in) int N = scanner.nextInt(); N scanner.nextInt() scanner.nextInt scanner int[] A = new int[N]; A new int[N] N int[] B = new int[N]; B new int[N] N int sum = 0; sum 0 A[0] = scanner.nextInt() A[0] A 0 scanner.nextInt() scanner.nextInt scanner int l = A[0]; l A[0] A 0 for(int i = 1; i < N; i ++) {
            A[i] = scanner.nextInt();
            l = lcm(l, A[i]);
        } int i = 1; int i = 1; i 1 i < N i N i ++ i ++ i {
            A[i] = scanner.nextInt();
            l = lcm(l, A[i]);
        } {
            A[i] = scanner.nextInt();
            l = lcm(l, A[i]);
        } A[i] = scanner.nextInt() A[i] A i scanner.nextInt() scanner.nextInt scanner l = lcm(l, A[i]) l lcm(l, A[i]) lcm l A[i] A i for(int i = 0; i < N; i ++) {
           B[i] = l / A[i];
           sum += B[i];
        } int i = 0; int i = 0; i 0 i < N i N i ++ i ++ i {
           B[i] = l / A[i];
           sum += B[i];
        } {
           B[i] = l / A[i];
           sum += B[i];
        } B[i] = l / A[i] B[i] B i l / A[i] l A[i] A i sum += B[i] sum B[i] B i System.out.println((double)l/sum) System.out.println System.out System System.out (double)l/sum (double)l sum static int lcm (int a, int b) {
        int temp;
        long c = a;
        c *= b;
        while((temp = a%b)!=0) {
            a = b;
            b = temp;
        }
        return (int)(c/b);
    } lcm {
        int temp;
        long c = a;
        c *= b;
        while((temp = a%b)!=0) {
            a = b;
            b = temp;
        }
        return (int)(c/b);
    } int temp; temp long c = a; c a c *= b c b while((temp = a%b)!=0) {
            a = b;
            b = temp;
        } (temp = a%b)!=0 (temp = a%b) temp a%b a b 0 {
            a = b;
            b = temp;
        } a = b a b b = temp b temp return (int)(c/b); (int)(c/b) c b int a a int b b public class Main {
    public static void main(String[] args){
        new Main().run();
    }

    private void run() {
        Scanner scanner = new Scanner(System.in);
        int N = scanner.nextInt();
        int[] A = new int[N];
        int[] B = new int[N];
        int sum = 0;
        A[0] = scanner.nextInt();
        int l = A[0];

        for(int i = 1; i < N; i ++) {
            A[i] = scanner.nextInt();
            l = lcm(l, A[i]);
        }
        for(int i = 0; i < N; i ++) {
           B[i] = l / A[i];
           sum += B[i];
        }

        System.out.println((double)l/sum);
    }

    static int lcm (int a, int b) {
        int temp;
        long c = a;
        c *= b;
        while((temp = a%b)!=0) {
            a = b;
            b = temp;
        }
        return (int)(c/b);
    }

} public class Main {
    public static void main(String[] args){
        new Main().run();
    }

    private void run() {
        Scanner scanner = new Scanner(System.in);
        int N = scanner.nextInt();
        int[] A = new int[N];
        int[] B = new int[N];
        int sum = 0;
        A[0] = scanner.nextInt();
        int l = A[0];

        for(int i = 1; i < N; i ++) {
            A[i] = scanner.nextInt();
            l = lcm(l, A[i]);
        }
        for(int i = 0; i < N; i ++) {
           B[i] = l / A[i];
           sum += B[i];
        }

        System.out.println((double)l/sum);
    }

    static int lcm (int a, int b) {
        int temp;
        long c = a;
        c *= b;
        while((temp = a%b)!=0) {
            a = b;
            b = temp;
        }
        return (int)(c/b);
    }

} Main
import java.util.Scanner;

public class Main {
    public static void main(String[] args){
        new Main().run();
    }

    private void run() {
        Scanner scanner = new Scanner(System.in);
        int N = scanner.nextInt();
        int[] A = new int[N];
        int[] B = new int[N];
        int sum = 0;
        A[0] = scanner.nextInt();
        int l = A[0];

        for(int i = 1; i < N; i ++) {
            A[i] = scanner.nextInt();
            l = lcm(l, A[i]);
        }
        for(int i = 0; i < N; i ++) {
           B[i] = l / A[i];
           sum += B[i];
        }

        System.out.println((double)l/sum);
    }

    static int lcm (int a, int b) {
        int temp;
        long c = a;
        c *= b;
        while((temp = a%b)!=0) {
            a = b;
            b = temp;
        }
        return (int)(c/b);
    }

}