// Template
#include "bits/stdc++.h"
#define rep_override(x, y, z, name, ...) name
#define rep2(i, n) for (int i = 0; i < (int)(n); ++i)
#define rep3(i, l, r) for (int i = (int)(l); i < (int)(r); ++i)
#define rep(...) rep_override(__VA_ARGS__, rep3, rep2)(__VA_ARGS__)
#define per(i, n) for (int i = (int)(n) - 1; i >= 0; --i)
#define all(x) (x).begin(), (x).end()
using namespace std;
using ll = long long;
constexpr int inf = 1001001001;
constexpr ll INF = 3003003003003003003LL;
template <typename T>
inline bool chmin(T &x, const T &y) {
    if (x > y) {
        x = y;
        return true;
    }
    return false;
}
template <typename T> 
inline bool chmax(T &x, const T &y) {
    if (x < y) {
        x = y;
        return true;
    }
    return false;
}
struct IOSET {
    IOSET() {
        cin.tie(nullptr);
        ios::sync_with_stdio(false);
        cout << fixed << setprecision(10);
    }
} ioset;
template <typename T>
istream &operator>>(istream &is, vector<T> &vec) {
    for (T &element : vec) is >> element;
    return is;
}
template <typename T>
ostream &operator<<(ostream &os, vector<T> &vec) {
    for (int i = 0, vec_len = (int)vec.size(); i < vec_len; ++i) {
        os << vec[i] << " \n"[i + 1 == vec_len];
    }
    return os;
}

// Main
int main() {
    int n, m;
    ll c;
    cin >> n >> m >> c;
    vector<ll> a(n), b(m);
    cin >> a >> b;
    
    sort(all(b));
    ll cnt = 0;
    rep(i, n) {
        int l = -1, r = m;
        while (r - l > 1) {
            int mid = (l + r) / 2;
            if (a[i] * b[mid] > c) r = mid;
            else l = mid;
        }
        cnt += m - r;
    }
    cout << (double) cnt / n / m << "\n";
}