import sys
read=sys.stdin.buffer.read
readline=sys.stdin.buffer.readline
readlines=sys.stdin.buffer.readlines

m=int(readline())
s=list(map(int, read().split()))
dp=[[] for _ in range(1<<(m+1))]
for i, x in enumerate(s):
    dp[i+(1<<m)].append([1.0, x*x])
for i in range((1<<m)-1, 0, -1):
    dp[i]=[[0.0, p[1]] for p in dp[2*i]+dp[2*i+1]]
    for j, x in enumerate(dp[2*i]):
        for k, y in enumerate(dp[2*i+1]):
            dp[i][j][0]+=x[0]*y[0]*(x[1]/(x[1]+y[1]))
            dp[i][len(dp[2*i])+k][0]+=x[0]*y[0]*(y[1]/(x[1]+y[1]))
print('{:.07f}'.format(dp[1][0][0]))