#include <bits/stdc++.h>

using namespace std;
// #include <atcoder/all>
// using namespace atcoder;
using ll =long long;
typedef pair<ll,ll> P;
#define SORT(a) sort((a).begin(),(a).end())
#define REV(a) reverse((a).begin(),(a).end())
#define For(i, a, b)    for(ll i = (a) ; i < (b) ; ++i)
#define rep(i, n)       For(i, 0, n)
#define debug(x)  cerr << #x << " = " << (x) << endl;
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; }

void coY() {cout <<"Yes"<<endl;}
void coN(){cout <<"No"<<endl;}
 
//Write From this Line


const ll dy[] = {0,0,1,-1};
const ll dx[] = {1,-1,0,0};
//const ll mod = 1e9+7;
//const ll mod = 998244353;
const double PI=3.14159265358979323846;
const ll INF = 1001001001;
int main()
{
	ll n, m, c;
	cin >> n >> m >> c;
	vector<ll> a(n);
	rep(i, n)cin>>a[i];
	vector<ll> b(m);
	rep(i, m)cin>>b[i];
	SORT(a);
	SORT(b);
	REV(b); // bは大きい順
	
	ll tmp = 0; // 尺取法のind
	vector<int> cnt(n);
	rep(i,n){
		ll x = a[i];
		// x * b[tmp] >= c なら tmp+1
		if(tmp == m){
			cnt[i] = tmp;
		} else {
			while(x * b[tmp] > c){
				tmp++;
				if(tmp == m) break;
			}
			cnt[i] = tmp;
		}
	}
	ll sum = 0;
	rep(i,n){
		sum += cnt[i];
	}
	debug(sum);
	cout << setprecision(15);
	cout << 1. *((double)sum / (double)(n*m)) << endl;
}