#include<bits/stdc++.h>
using namespace std;
using LL = long long;
using ULL = unsigned long long;
#define rep(i,n) for(int i=0; i<(n); i++)

int N, M;
LL C;
vector<LL> A, B;

int main() {
	cout << fixed << setprecision(10);

	cin >> N >> M >> C;
	A.resize(N); B.resize(M);
	rep(i, N) cin >> A[i];
	rep(i, M) cin >> B[i];

	sort(A.begin(), A.end());
	sort(B.begin(), B.end(), greater<LL>());

	LL ans = 0;

	rep(i, N) {
		int l = 0, r = M + 1;
		while (l + 1 < r) {
			int m = (l + r) / 2;
			if (A[i] * B[m - 1] > C) l = m; else r = m;
		}
		ans += l;
	}

	cout << (double(ans) / N / M) << endl;

	return 0;
}