import java.util.*;
public class Main {
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int wholeLcm = 1;
		int[] denominator = new int[n];
		int totalMolecule = 0;
		for(int i=0;i<n;i++){
			denominator[i] = sc.nextInt();
			wholeLcm = lcm(wholeLcm,denominator[i]);
		}
		
		for(int i=0;i<n;i++){
			totalMolecule += wholeLcm/denominator[i];
		}
		
        System.out.println((double)wholeLcm/totalMolecule);
	}
      
	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.*; util.* java public class Main {
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int wholeLcm = 1;
		int[] denominator = new int[n];
		int totalMolecule = 0;
		for(int i=0;i<n;i++){
			denominator[i] = sc.nextInt();
			wholeLcm = lcm(wholeLcm,denominator[i]);
		}
		
		for(int i=0;i<n;i++){
			totalMolecule += wholeLcm/denominator[i];
		}
		
        System.out.println((double)wholeLcm/totalMolecule);
	}
      
	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){
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int wholeLcm = 1;
		int[] denominator = new int[n];
		int totalMolecule = 0;
		for(int i=0;i<n;i++){
			denominator[i] = sc.nextInt();
			wholeLcm = lcm(wholeLcm,denominator[i]);
		}
		
		for(int i=0;i<n;i++){
			totalMolecule += wholeLcm/denominator[i];
		}
		
        System.out.println((double)wholeLcm/totalMolecule);
	} main {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int wholeLcm = 1;
		int[] denominator = new int[n];
		int totalMolecule = 0;
		for(int i=0;i<n;i++){
			denominator[i] = sc.nextInt();
			wholeLcm = lcm(wholeLcm,denominator[i]);
		}
		
		for(int i=0;i<n;i++){
			totalMolecule += wholeLcm/denominator[i];
		}
		
        System.out.println((double)wholeLcm/totalMolecule);
	} Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int n = sc.nextInt(); n sc.nextInt() sc.nextInt sc int wholeLcm = 1; wholeLcm 1 int[] denominator = new int[n]; denominator new int[n] n int totalMolecule = 0; totalMolecule 0 for(int i=0;i<n;i++){
			denominator[i] = sc.nextInt();
			wholeLcm = lcm(wholeLcm,denominator[i]);
		} int i=0; int i=0; i 0 i<n i n i++ i++ i {
			denominator[i] = sc.nextInt();
			wholeLcm = lcm(wholeLcm,denominator[i]);
		} {
			denominator[i] = sc.nextInt();
			wholeLcm = lcm(wholeLcm,denominator[i]);
		} denominator[i] = sc.nextInt() denominator[i] denominator i sc.nextInt() sc.nextInt sc wholeLcm = lcm(wholeLcm,denominator[i]) wholeLcm lcm(wholeLcm,denominator[i]) lcm wholeLcm denominator[i] denominator i for(int i=0;i<n;i++){
			totalMolecule += wholeLcm/denominator[i];
		} int i=0; int i=0; i 0 i<n i n i++ i++ i {
			totalMolecule += wholeLcm/denominator[i];
		} {
			totalMolecule += wholeLcm/denominator[i];
		} totalMolecule += wholeLcm/denominator[i] totalMolecule wholeLcm/denominator[i] wholeLcm denominator[i] denominator i System.out.println((double)wholeLcm/totalMolecule) System.out.println System.out System System.out (double)wholeLcm/totalMolecule (double)wholeLcm totalMolecule String[] args args 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){
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int wholeLcm = 1;
		int[] denominator = new int[n];
		int totalMolecule = 0;
		for(int i=0;i<n;i++){
			denominator[i] = sc.nextInt();
			wholeLcm = lcm(wholeLcm,denominator[i]);
		}
		
		for(int i=0;i<n;i++){
			totalMolecule += wholeLcm/denominator[i];
		}
		
        System.out.println((double)wholeLcm/totalMolecule);
	}
      
	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){
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int wholeLcm = 1;
		int[] denominator = new int[n];
		int totalMolecule = 0;
		for(int i=0;i<n;i++){
			denominator[i] = sc.nextInt();
			wholeLcm = lcm(wholeLcm,denominator[i]);
		}
		
		for(int i=0;i<n;i++){
			totalMolecule += wholeLcm/denominator[i];
		}
		
        System.out.println((double)wholeLcm/totalMolecule);
	}
      
	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.*;
public class Main {
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int wholeLcm = 1;
		int[] denominator = new int[n];
		int totalMolecule = 0;
		for(int i=0;i<n;i++){
			denominator[i] = sc.nextInt();
			wholeLcm = lcm(wholeLcm,denominator[i]);
		}
		
		for(int i=0;i<n;i++){
			totalMolecule += wholeLcm/denominator[i];
		}
		
        System.out.println((double)wholeLcm/totalMolecule);
	}
      
	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);
	}
}
