#include "bits/stdc++.h"
using namespace std;
//#include "atcoder/all"
//using namespace atcoder;
#define int long long
#define REP(i, n) for (int i = 0; i < (int)n; ++i)
#define RREP(i, n) for (int i = (int)n - 1; i >= 0; --i)
#define FOR(i, s, n) for (int i = s; i < (int)n; ++i)
#define RFOR(i, s, n) for (int i = (int)n - 1; i >= s; --i)
#define ALL(a) a.begin(), a.end()
#define IN(a, x, b) (a <= x && x < b)
template<class T>istream&operator >>(istream&is,vector<T>&vec){for(T&x:vec)is>>x;return is;}
template<class T>inline void out(T t){cout << t << "\n";}
template<class T,class... Ts>inline void out(T t,Ts... ts){cout << t << " ";out(ts...);}
template<class T>inline bool CHMIN(T&a,T b){if(a > b){a = b;return true;}return false;}
template<class T>inline bool CHMAX(T&a,T b){if(a < b){a = b;return true;}return false;}
constexpr int INF = 1e18;



signed main(){
	int N, M, C;
	cin >> N >> M >> C;
	vector<int> a(N), b(M);
	cin >> a >> b;
	sort(ALL(a));
	b.emplace_back(-INF);
	sort(ALL(b));
	double ans = 0;
	REP(i, N) {
		int tar = C / a[i];
		auto itr = lower_bound(ALL(b), tar + 1);
		ans += (1. / N) * (1.*(itr - b.begin() - 1) / M);
	}
	cout << setprecision(20) << 1. - ans << endl;
}