n,m,c = map(int,input().split())
a = list(map(int,input().split()))
b = list(map(int,input().split()))
count = 0
now = m-1
a.sort()
b.sort()

for i in a:
    while now >= 0 and i*b[now] > c:
        now -= 1
    count += m-now-1
print(count/(m*n))