import java.util.*;
import java.io.*;

class Main {
  public static void main(String[] args) {
    Scanner scan = new Scanner(System.in);
    int n = scan.nextInt();

    List<Integer> a = new ArrayList<Integer>();
    for(int i = 0; i < n; i++) {
      a.add(scan.nextInt());
    }

    double ans = 0.0;
    for(int i : a) ans += 1.0 / i;
    ans = 1.0 / ans;

    System.out.println(ans);
  }
} import java.util.*; util.* java import java.io.*; io.* java class Main {
  public static void main(String[] args) {
    Scanner scan = new Scanner(System.in);
    int n = scan.nextInt();

    List<Integer> a = new ArrayList<Integer>();
    for(int i = 0; i < n; i++) {
      a.add(scan.nextInt());
    }

    double ans = 0.0;
    for(int i : a) ans += 1.0 / i;
    ans = 1.0 / ans;

    System.out.println(ans);
  }
} Main public static void main(String[] args) {
    Scanner scan = new Scanner(System.in);
    int n = scan.nextInt();

    List<Integer> a = new ArrayList<Integer>();
    for(int i = 0; i < n; i++) {
      a.add(scan.nextInt());
    }

    double ans = 0.0;
    for(int i : a) ans += 1.0 / i;
    ans = 1.0 / ans;

    System.out.println(ans);
  } main {
    Scanner scan = new Scanner(System.in);
    int n = scan.nextInt();

    List<Integer> a = new ArrayList<Integer>();
    for(int i = 0; i < n; i++) {
      a.add(scan.nextInt());
    }

    double ans = 0.0;
    for(int i : a) ans += 1.0 / i;
    ans = 1.0 / ans;

    System.out.println(ans);
  } Scanner scan = new Scanner(System.in); scan new Scanner(System.in) int n = scan.nextInt(); n scan.nextInt() scan.nextInt scan List<Integer> a = new ArrayList<Integer>(); a new ArrayList<Integer>() for(int i = 0; i < n; i++) {
      a.add(scan.nextInt());
    } int i = 0; int i = 0; i 0 i < n i n i++ i++ i {
      a.add(scan.nextInt());
    } {
      a.add(scan.nextInt());
    } a.add(scan.nextInt()) a.add a scan.nextInt() scan.nextInt scan double ans = 0.0; ans 0.0 for(int i : a) ans += 1.0 / i; int i a ans += 1.0 / i; ans += 1.0 / i ans 1.0 / i 1.0 i ans = 1.0 / ans ans 1.0 / ans 1.0 ans System.out.println(ans) System.out.println System.out System System.out ans String[] args args
import java.util.*;
import java.io.*;

class Main {
  public static void main(String[] args) {
    Scanner scan = new Scanner(System.in);
    int n = scan.nextInt();

    List<Integer> a = new ArrayList<Integer>();
    for(int i = 0; i < n; i++) {
      a.add(scan.nextInt());
    }

    double ans = 0.0;
    for(int i : a) ans += 1.0 / i;
    ans = 1.0 / ans;

    System.out.println(ans);
  }
}