N=int(input())
A=[int(x) for x in input().split()]
s=[0]*(1<<N)
for i in range(1<<N):
    for j in range(N):
        if (i&(1<<j))>0:
            s[i]+=A[j]
dp={}
def f(a,b,t):
    if (a|b)==(1<<N)-1:
        return 1 if 2*s[a]+t>2*s[b] else 0
    c=int((a|(b<<N))*t)
    if c in dp:
        return dp[c]
    ret=0
    for i in range(N):
        na=a|(1<<i)
        if (na|b)==(a|b):
            continue
        e=1
        for j in range(N):
            nb=b|(1<<j)
            if (a|nb)==(a|b):
                continue
            p,q=A[i],A[j]
            v=1/p-f(b,na,t*(-1))/p+f(a,nb,t)/q*(1-1/p)
            v/=(p+q-1)/(p*q)
            e=min(e,v)
        ret=max(ret,e)
    dp[c]=ret
    return ret
print(f(0,0,-1))