#include <bits/stdc++.h>
using namespace std;
typedef long long int ll;
typedef pair<ll,ll> P;
typedef vector<ll> VI;
typedef vector<VI> VVI;
#define REP(i,n) for(int i=0;i<n;i++)
#define ALL(v) v.begin(),v.end()
const ll MOD=1000000007;
const ll INF=1e18;

int main(){
	ll n, m, c; cin >> n >> m >> c;
	VI a(n), b(m);
	REP(i,n) cin >> a[i];
	REP(i,m) cin >> b[i];
	sort(ALL(a));
	sort(ALL(b));
	ll sum=0;
	REP(i,n){
		sum+=m-(lower_bound(ALL(b),(c+a[i])/a[i])-b.begin());
	}
	cout << setprecision(10) << (double)sum/n/m << endl;
	return 0;
}