N, M, C = map(int, input().split())
A = list(map(int, input().split()))
B = list(map(int, input().split()))
cnt = 0
B.sort()
for i in range(N):
    if A[i] * B[0] > C:
        cnt += 0
    elif A[i] * B[-1] <= C:
        cnt += M
    else:
        l, r = 0, M
        d = (l + r) // 2
        for j in range(len(bin(M))):
            if A[i] * B[d] <= C:
                l = d
                d = (l + r) // 2
            else:
                r = d
                d = (l + r) // 2
        cnt += d + 1
print((N*M-cnt)/(N*M))