n, m, c = map(int, input().split())
a = list(map(int, input().split()))
b = list(map(int, input().split())) + [10 ** 18]
b.sort(reverse=True)
t = 0
for x in a:
    l, r = 0, m + 1
    while r - l > 1:
        mid = (l + r) // 2
        if x * b[mid] > c:
            l = mid
        else:
            r = mid
    t += l
print(t / (n * m))