#include <stdio.h>
#include <bits/stdc++.h>
using namespace std;
#define rep(i,n) for (int i = 0; i < (n); ++i)
#define Inf 1000000000

int main(){
	
	int N,M;
	cin>>N>>M;
	
	long long C;
	cin>>C;
	
	vector<long long> a(N),b(M);
	
	rep(i,N)cin>>a[i];
	rep(i,M)cin>>b[i];
	
	sort(a.begin(),a.end());
	sort(b.begin(),b.end());
	
	long double ans = 0.0;
	
	rep(i,N){
		long long x = (C+a[i])/a[i];
		long long y = distance(lower_bound(b.begin(),b.end(),x),b.end());
		
		long double Add = (long double)y;
		Add /= (long double)N;
		Add /= (long double)M;
		
		ans += Add;
	}
	
	cout<<fixed<<setprecision(10)<<ans<<endl;
	
    return 0;
}