#include <iostream>
#include <iomanip>
#include <algorithm>
#include <vector>

using lint = long long;
using ldouble = long double;

void solve() {
    int n, m;
    lint c;
    std::cin >> n >> m >> c;

    std::vector<lint> xs(n), ys(m);
    for (auto& x : xs) std::cin >> x;
    for (auto& y : ys) std::cin >> y;
    std::sort(ys.begin(), ys.end());

    lint ans = 0;
    for (auto x : xs) {
        lint l = c / x;
        ans += ys.end() - std::upper_bound(ys.begin(), ys.end(), l);
    }

    std::cout << ldouble(ans) / (ldouble(n) * m) << "\n";
}

int main() {
    std::cin.tie(nullptr);
    std::ios::sync_with_stdio(false);
    std::cout << std::fixed << std::setprecision(10);

    solve();

    return 0;
}