#include <iostream>
#include <vector>
#include <algorithm>
#include <iomanip>
using namespace std;
int main(){
    int n,m;
    long long c;cin>>n>>m>>c;
    vector<long long> A(n),B(m);
    for(int i = 0;n > i; i++){
        cin>>A[i];
    }
    for(int i = 0; m > i; i++){
        cin>>B[i];
    }
    sort(B.begin(),B.end());
    long long ans = 0;
    for(int i = 0; n > i; i++){
        ans += B.end()-lower_bound(B.begin(),B.end(),(c+A[i])/A[i]);
       // cout << (c+A[i]-1)/A[i] << " " << ans << endl;
    }
    cout << fixed << setprecision(10) << (double)ans/(n*m) << endl;
}