import java.util.*;
import java.math.BigDecimal;
 
public class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    int n = sc.nextInt();
    double ary[] = new double[n];
    double ans = 0;
    
    for (int i = 0; i < n; i++) { 
      ary[i] = sc.nextDouble(); 
      ans += 1 / ary[i];
    }
    
    ans = 1 / ans;
    
    System.out.println(ans);
  }
}
 import java.util.*; util.* java import java.math.BigDecimal; BigDecimal java.math public class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    int n = sc.nextInt();
    double ary[] = new double[n];
    double ans = 0;
    
    for (int i = 0; i < n; i++) { 
      ary[i] = sc.nextDouble(); 
      ans += 1 / ary[i];
    }
    
    ans = 1 / ans;
    
    System.out.println(ans);
  }
} Main public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    int n = sc.nextInt();
    double ary[] = new double[n];
    double ans = 0;
    
    for (int i = 0; i < n; i++) { 
      ary[i] = sc.nextDouble(); 
      ans += 1 / ary[i];
    }
    
    ans = 1 / ans;
    
    System.out.println(ans);
  } main {
    Scanner sc = new Scanner(System.in);
    int n = sc.nextInt();
    double ary[] = new double[n];
    double ans = 0;
    
    for (int i = 0; i < n; i++) { 
      ary[i] = sc.nextDouble(); 
      ans += 1 / ary[i];
    }
    
    ans = 1 / ans;
    
    System.out.println(ans);
  } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int n = sc.nextInt(); n sc.nextInt() sc.nextInt sc double ary[] = new double[n]; ary new double[n] n double ans = 0; ans 0 for (int i = 0; i < n; i++) { 
      ary[i] = sc.nextDouble(); 
      ans += 1 / ary[i];
    } int i = 0; int i = 0; i 0 i < n i n i++ i++ i { 
      ary[i] = sc.nextDouble(); 
      ans += 1 / ary[i];
    } { 
      ary[i] = sc.nextDouble(); 
      ans += 1 / ary[i];
    } ary[i] = sc.nextDouble() ary[i] ary i sc.nextDouble() sc.nextDouble sc ans += 1 / ary[i] ans 1 / ary[i] 1 ary[i] ary i ans = 1 / ans ans 1 / ans 1 ans System.out.println(ans) System.out.println System.out System System.out ans String[] args args public class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    int n = sc.nextInt();
    double ary[] = new double[n];
    double ans = 0;
    
    for (int i = 0; i < n; i++) { 
      ary[i] = sc.nextDouble(); 
      ans += 1 / ary[i];
    }
    
    ans = 1 / ans;
    
    System.out.println(ans);
  }
} public class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    int n = sc.nextInt();
    double ary[] = new double[n];
    double ans = 0;
    
    for (int i = 0; i < n; i++) { 
      ary[i] = sc.nextDouble(); 
      ans += 1 / ary[i];
    }
    
    ans = 1 / ans;
    
    System.out.println(ans);
  }
} Main
import java.util.*;
import java.math.BigDecimal;
 
public class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    int n = sc.nextInt();
    double ary[] = new double[n];
    double ans = 0;
    
    for (int i = 0; i < n; i++) { 
      ary[i] = sc.nextDouble(); 
      ans += 1 / ary[i];
    }
    
    ans = 1 / ans;
    
    System.out.println(ans);
  }
}

