import java.io.FileNotFoundException;
import java.math.BigDecimal;
import java.util.Scanner;

public class Main {
	@SuppressWarnings("deprecation")
	public static void main(String[] args) throws FileNotFoundException {

		//    	File file = new File("src/in.txt");
		//    	Scanner sc = new Scanner(file);

		Scanner sc = new Scanner(System.in);

		int N = sc.nextInt();
		int[] A = new int[N];
		BigDecimal times = BigDecimal.valueOf(1);
		for(int i=0;i<N;i++) {
			A[i]=sc.nextInt();
			times = times.multiply(BigDecimal.valueOf(A[i]));
		}
		BigDecimal q = BigDecimal.valueOf(0);
		for(int i=0;i<N;i++) {
			BigDecimal x = times.divide(BigDecimal.valueOf(A[i]));
			q = q.add(x);
		}
		System.out.println(times.divide(q,6, BigDecimal.ROUND_HALF_UP));

	}
} import java.io.FileNotFoundException; FileNotFoundException java.io import java.math.BigDecimal; BigDecimal java.math import java.util.Scanner; Scanner java.util public class Main {
	@SuppressWarnings("deprecation")
	public static void main(String[] args) throws FileNotFoundException {

		//    	File file = new File("src/in.txt");
		//    	Scanner sc = new Scanner(file);

		Scanner sc = new Scanner(System.in);

		int N = sc.nextInt();
		int[] A = new int[N];
		BigDecimal times = BigDecimal.valueOf(1);
		for(int i=0;i<N;i++) {
			A[i]=sc.nextInt();
			times = times.multiply(BigDecimal.valueOf(A[i]));
		}
		BigDecimal q = BigDecimal.valueOf(0);
		for(int i=0;i<N;i++) {
			BigDecimal x = times.divide(BigDecimal.valueOf(A[i]));
			q = q.add(x);
		}
		System.out.println(times.divide(q,6, BigDecimal.ROUND_HALF_UP));

	}
} Main @SuppressWarnings("deprecation")
	public static void main(String[] args) throws FileNotFoundException {

		//    	File file = new File("src/in.txt");
		//    	Scanner sc = new Scanner(file);

		Scanner sc = new Scanner(System.in);

		int N = sc.nextInt();
		int[] A = new int[N];
		BigDecimal times = BigDecimal.valueOf(1);
		for(int i=0;i<N;i++) {
			A[i]=sc.nextInt();
			times = times.multiply(BigDecimal.valueOf(A[i]));
		}
		BigDecimal q = BigDecimal.valueOf(0);
		for(int i=0;i<N;i++) {
			BigDecimal x = times.divide(BigDecimal.valueOf(A[i]));
			q = q.add(x);
		}
		System.out.println(times.divide(q,6, BigDecimal.ROUND_HALF_UP));

	} main {

		//    	File file = new File("src/in.txt");
		//    	Scanner sc = new Scanner(file);

		Scanner sc = new Scanner(System.in);

		int N = sc.nextInt();
		int[] A = new int[N];
		BigDecimal times = BigDecimal.valueOf(1);
		for(int i=0;i<N;i++) {
			A[i]=sc.nextInt();
			times = times.multiply(BigDecimal.valueOf(A[i]));
		}
		BigDecimal q = BigDecimal.valueOf(0);
		for(int i=0;i<N;i++) {
			BigDecimal x = times.divide(BigDecimal.valueOf(A[i]));
			q = q.add(x);
		}
		System.out.println(times.divide(q,6, BigDecimal.ROUND_HALF_UP));

	} Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int N = sc.nextInt(); N sc.nextInt() sc.nextInt sc int[] A = new int[N]; A new int[N] N BigDecimal times = BigDecimal.valueOf(1); times BigDecimal.valueOf(1) BigDecimal.valueOf BigDecimal 1 for(int i=0;i<N;i++) {
			A[i]=sc.nextInt();
			times = times.multiply(BigDecimal.valueOf(A[i]));
		} int i=0; int i=0; i 0 i<N i N i++ i++ i {
			A[i]=sc.nextInt();
			times = times.multiply(BigDecimal.valueOf(A[i]));
		} {
			A[i]=sc.nextInt();
			times = times.multiply(BigDecimal.valueOf(A[i]));
		} A[i]=sc.nextInt() A[i] A i sc.nextInt() sc.nextInt sc times = times.multiply(BigDecimal.valueOf(A[i])) times times.multiply(BigDecimal.valueOf(A[i])) times.multiply times BigDecimal.valueOf(A[i]) BigDecimal.valueOf BigDecimal A[i] A i BigDecimal q = BigDecimal.valueOf(0); q BigDecimal.valueOf(0) BigDecimal.valueOf BigDecimal 0 for(int i=0;i<N;i++) {
			BigDecimal x = times.divide(BigDecimal.valueOf(A[i]));
			q = q.add(x);
		} int i=0; int i=0; i 0 i<N i N i++ i++ i {
			BigDecimal x = times.divide(BigDecimal.valueOf(A[i]));
			q = q.add(x);
		} {
			BigDecimal x = times.divide(BigDecimal.valueOf(A[i]));
			q = q.add(x);
		} BigDecimal x = times.divide(BigDecimal.valueOf(A[i])); x times.divide(BigDecimal.valueOf(A[i])) times.divide times BigDecimal.valueOf(A[i]) BigDecimal.valueOf BigDecimal A[i] A i q = q.add(x) q q.add(x) q.add q x System.out.println(times.divide(q,6, BigDecimal.ROUND_HALF_UP)) System.out.println System.out System System.out times.divide(q,6, BigDecimal.ROUND_HALF_UP) times.divide times q 6 BigDecimal.ROUND_HALF_UP BigDecimal BigDecimal.ROUND_HALF_UP String[] args args public class Main {
	@SuppressWarnings("deprecation")
	public static void main(String[] args) throws FileNotFoundException {

		//    	File file = new File("src/in.txt");
		//    	Scanner sc = new Scanner(file);

		Scanner sc = new Scanner(System.in);

		int N = sc.nextInt();
		int[] A = new int[N];
		BigDecimal times = BigDecimal.valueOf(1);
		for(int i=0;i<N;i++) {
			A[i]=sc.nextInt();
			times = times.multiply(BigDecimal.valueOf(A[i]));
		}
		BigDecimal q = BigDecimal.valueOf(0);
		for(int i=0;i<N;i++) {
			BigDecimal x = times.divide(BigDecimal.valueOf(A[i]));
			q = q.add(x);
		}
		System.out.println(times.divide(q,6, BigDecimal.ROUND_HALF_UP));

	}
} public class Main {
	@SuppressWarnings("deprecation")
	public static void main(String[] args) throws FileNotFoundException {

		//    	File file = new File("src/in.txt");
		//    	Scanner sc = new Scanner(file);

		Scanner sc = new Scanner(System.in);

		int N = sc.nextInt();
		int[] A = new int[N];
		BigDecimal times = BigDecimal.valueOf(1);
		for(int i=0;i<N;i++) {
			A[i]=sc.nextInt();
			times = times.multiply(BigDecimal.valueOf(A[i]));
		}
		BigDecimal q = BigDecimal.valueOf(0);
		for(int i=0;i<N;i++) {
			BigDecimal x = times.divide(BigDecimal.valueOf(A[i]));
			q = q.add(x);
		}
		System.out.println(times.divide(q,6, BigDecimal.ROUND_HALF_UP));

	}
} Main
import java.io.FileNotFoundException;
import java.math.BigDecimal;
import java.util.Scanner;

public class Main {
	@SuppressWarnings("deprecation")
	public static void main(String[] args) throws FileNotFoundException {

		//    	File file = new File("src/in.txt");
		//    	Scanner sc = new Scanner(file);

		Scanner sc = new Scanner(System.in);

		int N = sc.nextInt();
		int[] A = new int[N];
		BigDecimal times = BigDecimal.valueOf(1);
		for(int i=0;i<N;i++) {
			A[i]=sc.nextInt();
			times = times.multiply(BigDecimal.valueOf(A[i]));
		}
		BigDecimal q = BigDecimal.valueOf(0);
		for(int i=0;i<N;i++) {
			BigDecimal x = times.divide(BigDecimal.valueOf(A[i]));
			q = q.add(x);
		}
		System.out.println(times.divide(q,6, BigDecimal.ROUND_HALF_UP));

	}
}
