#include <iostream>
#include <string>
#include <algorithm>
#include <vector>
#include <iomanip>
#include <cmath>
#include <stdio.h>
#include <queue>
#include <deque>
#include <cstdio>
#include <set>
#include <map>
#include <bitset>
#include <stack>
#include <cctype>
using namespace std;
vector<long long> a, b;
int main() {
	long double n, m;
	long long c;
	cin >> n >> m >> c;
	for (int i = 0; i < n; i++) {
		long long a1;
		cin >> a1;
		a.emplace_back(a1);
	}
	for (int i = 0; i < m; i++) {
		long long b1;
		cin >> b1;
		b.emplace_back(b1);
	}
	sort(a.begin(), a.end());
	sort(b.begin(), b.end());
	long double co = 0;
	for (int i = 0; i < n; i++) {
		auto itr = upper_bound(b.begin(), b.end(), c / a[i]);
		co += int(b.end() - itr);
	}
	cout << fixed << setprecision(16) << co / (n * m) << endl;
}