#include <iostream>
#include <vector>
#include <algorithm>
#include <cmath>
#include <queue>
#include <string>
#include <map>
#include <set>
#include <stack>
#include <tuple>
#include <deque>
#include <array>
#include <numeric>
#include <bitset>
#include <iomanip>
#include <cassert>
#include <chrono>
#include <random>
#include <limits>
#include <iterator>
#include <functional>
#include <sstream>
#include <fstream>
#include <complex>
#include <cstring>
#include <unordered_map>
#include <unordered_set>
using namespace std;

using ll = long long;
using P = pair<int, int>;
constexpr int INF = 1001001001;
constexpr int mod = 1000000007;
// constexpr int mod = 998244353;

template<class T>
inline bool chmax(T& x, T y){
    if(x < y){
        x = y;
        return true;
    }
    return false;
}
template<class T>
inline bool chmin(T& x, T y){
    if(x > y){
        x = y;
        return true;
    }
    return false;
}

int main(){
    ios::sync_with_stdio(false);
    cin.tie(nullptr);

    int N, M;
    ll C;
    cin >> N >> M >> C;
    vector<int> 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(b.begin(), b.end());
    
    double ans = 0.0;
    for(int i = 0; i < N; ++i){
        ans += end(b) - upper_bound(begin(b), end(b), C / a[i]);
    }
    ans /= N * M;

    cout << fixed << setprecision(15);
    cout << ans << endl;

    return 0;
}