#include <bits/stdc++.h>

typedef unsigned long long ULLONG;
typedef long long LLONG;
static const LLONG MOD_NUM = 1000000007LL; //998244353LL;
static const LLONG INF_NUM = 1000000007LL;

template<class _T> static void get(_T& a) {
	std::cin >> a;
}
template<class _T> static void get(_T& a, _T& b) {
	std::cin >> a >> b;
}
template<class _T> static void get(_T& a, _T& b, _T& c) {
	std::cin >> a >> b >> c;
}
template <class _T> static _T tp_abs(_T a) {
	if (a < (_T)0) {
		a *= (_T)-1;
	}
	return a;
}
template <class _T> static _T tp_pow(int base, int exp)
{
	_T ans = 1;

	for (int i = 0; i < exp; i++) {
		ans *= (_T)base;
	}
	return ans;
}

static void A_task();

int main()
{
	A_task();
	fflush(stdout);
	return 0;
}

static void A_task()
{
	int N, M;
	LLONG C;

	get(N, M);
	get(C);

	std::vector<LLONG> ai(N), bi(M);
	for (int i = 0; i < N; i++) {
		get(ai[i]);
	}
	for (int i = 0; i < M; i++) {
		get(bi[i]);
	}

	std::sort(ai.begin(), ai.end());
	std::sort(bi.begin(), bi.end());

	LLONG cnt = 0;
	for (int i = 0; i < N; i++) {
		LLONG th = C / ai[i];
		auto targ = std::upper_bound(bi.begin(), bi.end(), th);
		cnt += M - (targ - bi.begin());
	}

	printf("%.9lF\n", (long double)cnt / (long double)(N * M));
}