import java.util.Arrays;
import java.util.PriorityQueue;
import java.util.Scanner;

class Main {
	public static void main(String[] args) {
		new Main().run();
	}
	
	void run() {
		Scanner sc=new Scanner(System.in);
		int M=sc.nextInt();
		double[] S=new double[1<<M];
		for(int i=0;i<1<<M;++i)S[i]=sc.nextDouble();
		for(int i=0;i<1<<M;++i)S[i]=S[i]*S[i];
		double[][] P=new double[1<<M][M+1];
		for(int i=0;i<1<<M;++i)P[i][0]=1;
		for(int i=0;i<M;++i) {
			for(int a=0;a<1<<M;++a) {
				for(int b=0;b<1<<M;++b) {
					if((a>>(i+1))!=(b>>(i+1)))continue;
					if((a>>i)%2==(b>>i)%2)continue;
					P[a][i+1]+=P[a][i]*P[b][i]*S[a]/(S[a]+S[b]);
				}
			}
		}
		System.out.println(P[0][M]);
	}
	
	static void tr(Object... objects) {
		System.out.println(Arrays.deepToString(objects));
	}

}