N = int(input())
A = [int(a) for a in input().split()]
assert 1 <= N <= 10
assert len(A) == N
for a in A:
    assert 1 <= N <= 20

D = {}
def prob(i, j, s, t, h):
    p, q, a, b = 1 / A[i], 1 / A[j], 1 - calc(s ^ (1 << i), h + 1 - t), calc(s ^ (1 << j), t)
    x = (p * a + (1 - p) * q * b) / (p + q - p * q)
    return x
def calc(s, t):
    if t <= 0: return 1
    if s == 0: return 0
    y = s + (t << N)
    if y in D: return D[y]
    h = sum([A[i] for i in range(N) if s >> i & 1])
    D[y] = max([min([prob(i, j, s, t, h) for j in range(N) if s >> j & 1] + [1]) for i in range(N) if s >> i & 1] + [0])
    return D[y]
print(calc((1 << N) - 1, sum(A) // 2 + 1))