import java.util.*;
public class Main{
	public static void main(String[] arugs){
		Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();
		double[] A = new double[N];
		double ans = 0;
		double sum = 0;
		double result = 0;
		
		for(int i=0; i<N; i++){
			A[i] = sc.nextDouble();
		}
		
		for(int j=0; j<N; j++){
			ans = 1/A[j];
			sum += ans;
			ans = 0;
		}
		
		result = 1/sum;
		
		System.out.println(result);
	}
} import java.util.*; util.* java public class Main{
	public static void main(String[] arugs){
		Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();
		double[] A = new double[N];
		double ans = 0;
		double sum = 0;
		double result = 0;
		
		for(int i=0; i<N; i++){
			A[i] = sc.nextDouble();
		}
		
		for(int j=0; j<N; j++){
			ans = 1/A[j];
			sum += ans;
			ans = 0;
		}
		
		result = 1/sum;
		
		System.out.println(result);
	}
} Main public static void main(String[] arugs){
		Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();
		double[] A = new double[N];
		double ans = 0;
		double sum = 0;
		double result = 0;
		
		for(int i=0; i<N; i++){
			A[i] = sc.nextDouble();
		}
		
		for(int j=0; j<N; j++){
			ans = 1/A[j];
			sum += ans;
			ans = 0;
		}
		
		result = 1/sum;
		
		System.out.println(result);
	} main {
		Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();
		double[] A = new double[N];
		double ans = 0;
		double sum = 0;
		double result = 0;
		
		for(int i=0; i<N; i++){
			A[i] = sc.nextDouble();
		}
		
		for(int j=0; j<N; j++){
			ans = 1/A[j];
			sum += ans;
			ans = 0;
		}
		
		result = 1/sum;
		
		System.out.println(result);
	} Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int N = sc.nextInt(); N sc.nextInt() sc.nextInt sc double[] A = new double[N]; A new double[N] N double ans = 0; ans 0 double sum = 0; sum 0 double result = 0; result 0 for(int i=0; i<N; i++){
			A[i] = sc.nextDouble();
		} int i=0; int i=0; i 0 i<N i N i++ i++ i {
			A[i] = sc.nextDouble();
		} {
			A[i] = sc.nextDouble();
		} A[i] = sc.nextDouble() A[i] A i sc.nextDouble() sc.nextDouble sc for(int j=0; j<N; j++){
			ans = 1/A[j];
			sum += ans;
			ans = 0;
		} int j=0; int j=0; j 0 j<N j N j++ j++ j {
			ans = 1/A[j];
			sum += ans;
			ans = 0;
		} {
			ans = 1/A[j];
			sum += ans;
			ans = 0;
		} ans = 1/A[j] ans 1/A[j] 1 A[j] A j sum += ans sum ans ans = 0 ans 0 result = 1/sum result 1/sum 1 sum System.out.println(result) System.out.println System.out System System.out result String[] arugs arugs public class Main{
	public static void main(String[] arugs){
		Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();
		double[] A = new double[N];
		double ans = 0;
		double sum = 0;
		double result = 0;
		
		for(int i=0; i<N; i++){
			A[i] = sc.nextDouble();
		}
		
		for(int j=0; j<N; j++){
			ans = 1/A[j];
			sum += ans;
			ans = 0;
		}
		
		result = 1/sum;
		
		System.out.println(result);
	}
} public class Main{
	public static void main(String[] arugs){
		Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();
		double[] A = new double[N];
		double ans = 0;
		double sum = 0;
		double result = 0;
		
		for(int i=0; i<N; i++){
			A[i] = sc.nextDouble();
		}
		
		for(int j=0; j<N; j++){
			ans = 1/A[j];
			sum += ans;
			ans = 0;
		}
		
		result = 1/sum;
		
		System.out.println(result);
	}
} Main
import java.util.*;
public class Main{
	public static void main(String[] arugs){
		Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();
		double[] A = new double[N];
		double ans = 0;
		double sum = 0;
		double result = 0;
		
		for(int i=0; i<N; i++){
			A[i] = sc.nextDouble();
		}
		
		for(int j=0; j<N; j++){
			ans = 1/A[j];
			sum += ans;
			ans = 0;
		}
		
		result = 1/sum;
		
		System.out.println(result);
	}
}
