M = int(input())
S = [int(input()) for _ in range(2**M)]
dp = [[0] * (2**M) for _ in range(M+1)]

for i in range(2**M):
    dp[0][i] = 1

for i in range(M):
    for j in range(2**M):
        for k in range(2**M):
            if (j^k)>>i == 1:
                dp[i+1][j] += dp[i][k]*S[j]**2/(S[j]**2+S[k]**2)
                
        dp[i+1][j] *= dp[i][j]

print(dp[M][0])