m = int(input())
S = [int(input()) for _ in range(2**m)]

total = 2**m
DP = [1.0 for _ in range(total)]
for i in range(m):
    NDP = [0.0 for _ in range(total)]
    for j in range(total):
        for k in range(total):
            if j >> (i + 1) != k >> (i + 1):
                continue
            if (j >> i) & 1 != (k >> i) & 1:
                NDP[j] += S[j]**2 / (S[j]**2 + S[k]**2) * DP[j] * DP[k]
    DP = NDP
print(DP[0])