from collections import defaultdict

def rec(l, r):
    d = defaultdict(int)
    
    if l == r:
        d[l] = 1.0
        return d
        
    dl = rec(l, (l+r)//2)
    dr = rec((l+r)//2+1, r)
    
    for k, v in dl.items():
        prob = 0
        
        for k2, v2 in dr.items():
            prob += v2*S[k]**2/(S[k]**2+S[k2]**2)
        
        d[k] = v*prob
    
    for k, v in dr.items():
        prob = 0
        
        for k2, v2 in dl.items():
            prob += v2*S[k]**2/(S[k]**2+S[k2]**2)
        
        d[k] = v*prob
    
    return d
    
M = int(input())
S = [int(input()) for _ in range(2**M)]
d = rec(0, 2**M-1)

print(d[0])