import java.util.*;
public class Main {	
	public static void main(String args[]){
		Scanner sc = new Scanner(System.in);
		int aa = sc.nextInt();
		double x[] = new double[aa];
		for(int n = 0; n < aa; n++){
			x[n] = sc.nextInt();
		}
		double a = 1;
		double b = x[0];
		for(int n=1; n < aa; n++){
			a = a*x[n] + b;
			b *= x[n];
			double t = f(Math.max(a, b), Math.min(a, b));
			a = a / t;
			b = b / t;
		}
		System.out.println((double)b/(double)a);
		
		
	}
	
	public static double f(double d, double e){
		double t = d % e;
		if(t == 1)return 1;
		else if(t == 0)return e;
		else return f(e, t);
	}
}
/tmp/hf-datasets-cache/medium/datasets/42704881117311-config-parquet-and-info-qiankunmu-Project_CodeNet-896c9d36/hub/datasets--qiankunmu--Project_CodeNet_Python800_and_Java250/snapshots/c899fde44a77ba1cc14973ed3de064e4ff3aadc7/Project_CodeNet_Java250.tar.gz