import java.util.Scanner;


public class Main_yukicoder66 {

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);

        int m = sc.nextInt();
        int n = 0x1 << m;
        int[] s = new int[n];

        for (int i = 0; i < n; i++) {
        	s[i] = sc.nextInt();
        }

        double[][] p = new double[m][n];

        for (int i = 0; i < m; i++) {
        	for (int j = 0; j < n; j++) {
        		for (int k = 0; k < n; k++) {
        			int mask = ~((0x1 << i + 1) - 1);
        			int bit = 0x1 << i;
        			if ((j & bit) == (k & bit)) {
        				continue;
        			}
        			if ((j & mask) != (k & mask)) {
        				continue;
        			}

            		if (i > 0) {
            			p[i][j] += p[i - 1][j] * p[i - 1][k] * s[j] * s[j] / (s[j] * s[j] + s[k] * s[k]);
        			} else {
        				p[i][j] += (double)s[j] * s[j] / (s[j] * s[j] + s[k] * s[k]);
        			}
        		}

        	}
        }

        System.out.printf("%.7f\n", p[m - 1][0]);

        sc.close();
    }
}