N,M,C=map(int, input().split())
a_ls=list(map(int, input().split()))
b_ls=list(map(int, input().split()))

a_ls.sort(reverse=True)
b_ls.sort()
i=0
ans=0
for a in a_ls:
	while a*b_ls[i]<=C:
		i+=1
		if i==M:
			i=M-1
			break
	
	if i==M-1 and a*b_ls[M-1]<=C:
		ans+=0
	else:
		ans+=(M-i)

print(float(ans)/(N*M))