import sys
input=lambda:sys.stdin.readline().rstrip()
M=int(input())
S=[int(input()) for i in range(1<<M)]
prob=[[i==0 for j in range(1<<M)] for i in range(M+1)]
for i in range(1,M+1):
	for j in range(1<<M):
		start=(j>>(i-1))
		start+=1-2*(start%2)
		start<<=(i-1)
		for k in range(1<<(i-1)):
			prob[i][j]+=prob[i-1][start+k]*S[j]**2/(S[j]**2+S[start+k]**2)
		prob[i][j]*=prob[i-1][j]
print(prob[M][0])