#include <bits/stdc++.h>
using namespace std;

int main() {
    int n, m;
    long long c;
    cin >> n >> m >> c;
    vector<long long> a(n), b(m);
    for(auto &e : a) cin >> e;
    for(auto &e : b) cin >> e;
    sort(b.begin(), b.end());
    long long cnt = 0;
    for(auto &x : a) {
        cnt += b.end() - upper_bound(b.begin(), b.end(), c / x);
    }
    double ans = cnt / (double(n) * m);
    printf("%.15lf\n", ans);
    return 0;
}