n = int(input())
assert 2 <= n <= 100
a = list(map(int, input().split()))
assert n - 1 == len(a)
x = 1000
y = 1
for i in a:
    assert 0 <= i <= 10
    x *= 1000 - i
    y *= 1000
x = 1000 * y - x
while x % 10 == 0:
    x //= 10
    y //= 10
xx = str(x)
m = len(str(x)) - len(str(y)) + 1
print(xx[:m] + "." + xx[m:])