from sys import stdin

N,M,C = map(int,stdin.readline().split())
a = list(map(int,stdin.readline().split()))
b = list(map(int,stdin.readline().split()))

b.sort()
ans = 0

for i in range(N):

    na = a[i]
    l = -1
    r = M

    while r-l != 1:

        m = (l+r)//2

        if b[m] * na > C:
            r = m
        else:
            l = m

    ans += r

print (1 - ans / (N*M))