#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
int main() {
	ll N,M,C;
	cin >> N >> M >> C;
	vector<ll> a(N);
	vector<ll> b(M);
	for(ll i = 0;i < N;i++)cin >> a[i];
	for(ll i = 0;i < M;i++)cin >> b[i];

	sort(a.begin(),a.end());
	sort(b.begin(),b.end());

	ll num = 0;
	for(ll i = 0;i < N;i++){
		auto p = upper_bound(b.begin(),b.end(),C/a[i]);
		num += b.end() - p;
	}

	double ans = (double)(num)/(N * M);
	printf("%.14lf\n",ans);
}