import java.util.*;

public class Main {
	public static void main (String[] args) {
		Scanner sc = new Scanner(System.in);
		int m = sc.nextInt();
		double[] powers = new double[1 << m];
		for (int i = 0; i < (1 << m); i++) {
		    powers[i] = Math.pow(sc.nextInt(), 2);
		}
		double[][] dp = new double[m + 1][1 << m];
		Arrays.fill(dp[0], 1.0);
		for (int i = 1; i <= m; i++) {
		    for (int j = 0; j < (1 << m); j++) {
		        int base = ((j >> (i - 1)) ^ 1) << (i - 1);
		        for (int k = 0; k < (1 << (i - 1)); k++) {
		            dp[i][j] += dp[i - 1][base + k] * (powers[j] / (powers[j] + powers[base + k]));
		        }
		        dp[i][j] *= dp[i - 1][j];
		    }
		}
		System.out.println(dp[m][0]);
   }

}