#include <bits/stdc++.h>
#define range(i, l, r) for(int (i) = (l); (i) < (r); (i)++)
#define reversed_range(i, l, r) for (int (i) = (r) - 1; (i) >= l; (i)--)
using namespace std;
template <typename T>
using vec = vector<T>;
using lint = long long;
using ulint = unsigned long long;
using pint = pair<int, int>;
using plint = pair<lint, lint>;

template <typename S, typename T>
ostream& operator <<(ostream& os, pair<S, T> p) {
    os << "(";
    os << p.first << ", " << p.second;
    return os << ")";
}

template <typename T>
ostream& operator <<(ostream& os, vec<T> v) {
    os << "[";
    for (int i = 0; i < v.size() - 1; i++) {
        os << v.at(i) << ", ";
    }
    return os << v.at(v.size() - 1) << "]";
}

template <typename T>
ostream& operator <<(ostream& os, set<T>& s) {
    os << "{";
    auto it_first_item = s.begin();
    cout << *it_first_item;
    for (auto it = ++it_first_item; it != s.end(); it++) {
        cout << ", " << *it;
    }
    return cout << "}";
}

template <typename T>
ostream& operator <<(ostream& os, unordered_set<T>& s) {
    os << "{";
    auto it_first_item = s.begin();
    cout << *it_first_item;
    for (auto it = ++it_first_item; it != s.end(); it++) {
        cout << ", " << *it;
    }
    return cout << "}";
}

template <typename K, typename V>
ostream& operator <<(ostream& os, map<K, V> m) {
    os << "{";
    auto it_first_item = m.begin();
    cout << it_first_item->first << ": " << it_first_item->second;
    for (auto it = ++it_first_item; it != m.end(); it++) {
        cout << ", " << it->first << ": " << it->second;
    }
    return os << "}";
}

template <typename K, typename V>
ostream& operator <<(ostream& os, unordered_map<K, V> m) {
    os << "{";
    auto it_first_item = m.begin();
    cout << it_first_item->first << ": " << it_first_item->second;
    for (auto it = ++it_first_item; it != m.end(); it++) {
        cout << ", " << it->first << ": " << it->second;
    }
    return os << "}";
}

int main() {
    cin.tie(0); cout.tie(0);
    ios::sync_with_stdio(false);
    lint N;
    cin >> N;
    vec<lint> A_list(N);
    range(i, 0, N) cin >> A_list.at(i);
    sort(A_list.begin(), A_list.end());
    vec<lint> available_edges;
    lint prev_A = A_list.at(0);
    range(i, 1, N) {
        lint A = A_list.at(i);
        if (prev_A == A) {
            available_edges.emplace_back(A);
            prev_A = -1;
        } else {
            prev_A = A;
        }
    }
    if (available_edges.size() < 2) {
        cout << 0 << "\n";
    } else {
        lint num_edges = available_edges.size();
        cout << available_edges.at(num_edges - 1) * available_edges.at(num_edges - 2) << "\n";
    }
    // unordered_map<lint, lint> count_of;
    // for (const auto A : A_list) {
    //     count_of[A] += 1;
    // }
    // lint biggest_edge = 0, second_biggest_edge = 0;
    // for (const auto edge_with_count : count_of) {
    //     lint edge = edge_with_count.first;
    //     lint count = edge_with_count.second;
    //     if (count >= 2){
    //         if (edge > biggest_edge) {
    //             second_biggest_edge = biggest_edge;
    //             biggest_edge = edge;
    //         } else if (edge > second_biggest_edge) {
    //             second_biggest_edge = edge;
    //         }
    //     }
    // }
    // cout << biggest_edge * second_biggest_edge << "\n";
}

Measured memory_bytes: 1660