#!/usr/bin/env python3.8
import sys
read = sys.stdin.buffer.read
readline = sys.stdin.buffer.readline
readlines = sys.stdin.buffer.readlines
import numpy as np

M = int(readline())
S = np.array(read().split(), np.int64)
S **= 2

dp = np.ones(1 << M)
for i in range(M):
    newdp = np.empty(1 << M)
    n = 1 << i
    for j in range(1 << M):
        k = (1 ^ (j >> i)) << i
        win_per = S[j] / (S[k: k + n] + S[j])
        newdp[j] = dp[j] * (win_per * dp[k:k + n]).sum()
    dp = newdp
print(dp[0])