#yuki66

m=int(raw_input())
s=[1.0*int(raw_input()) for i in xrange(2**m)]
v=[[s[i]**2/(s[i]**2+s[j]**2) for j in xrange(2**m)] for i in xrange(2**m)]
dp=[[0 for i in xrange(2**m)] for j in xrange(m+1)]
for i in xrange(2**m):
 dp[0][i]=1
for i in xrange(1,m+1):
 for j in xrange(2**m):
  for k in xrange(2**m):
   if (j^k)>>(i-1) !=1:
    continue
   dp[i][j]+=dp[i-1][j]*dp[i-1][k]*v[j][k]
print dp[m][0]