n, m, c = map(int, input().split())
A = list(map(int, input().split()))
B = list(map(int, input().split()))

ab = []
C = []
for a in A:
    for b in B:
        ab.append(a*b)
        if a * b > c:
            C.append(a*b)

print(len(C)/len(ab))