#include <bits/stdc++.h>
using namespace std;
#include <boost/multiprecision/cpp_int.hpp>
typedef boost::multiprecision::cpp_int mp;


int main(){
    int N,M;
    long long C;
    cin>>N>>M>>C;
    vector<long long> A(N),B(M);
    for(int i=0;i<N;++i){
        cin>>A[i];
    }
    for(int i=0;i<M;++i){
        cin>>B[i];
    }
    sort(A.begin(),A.end());
    sort(B.begin(),B.end());
    long long ans=0;
    for(int i=0;i<N;i++){
        cerr<<A[i]<<endl;
        int l=-1,r=M;
        while(r-l>1){
            cerr<<l<<' '<<r<<endl;
            int m=(l+r)/2;
            cerr<<B[m]<<endl;
            if(C<B[m]*A[i]){
                r=m;
            }else{
                l=m;
            }
        }
        ans+=M-r;
    }
    cout<<((double)ans/(double)N/(double)M)<<endl;
}