#ifndef _DEBUG
#define _DEBUG
#include __FILE__

int main() {
    long N;
    cin >> N, N *= 2;
    vector<long> A(N);
    for (auto&& a : A) cin >> a;

    sort(A.begin(), A.end());
    reverse(A.begin(), A.end());

    long ans = 0;
    for (int i = 0; i + 1 < N; i += 2) {
        ans += A.at(i) * A.at(i + 1);
    }
    cout << ans << '\n';
}

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

template <typename T, typename T2>
bool cmin(T& a, const T2& b) {
    return a > b ? a = b, true : false;
}

template <typename T, typename T2>
bool cmax(T& a, const T2& b) {
    return a < b ? a = b, true : false;
}

__attribute__((constructor)) void ios_setup() {
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
}

template <typename T>
ostream& operator<<(ostream& os, const vector<T>& vec);

template <typename T>
ostream& operator<<(ostream& os, const vector<vector<T> >& vec);

template <typename T>
ostream& operator<<(ostream& os, const vector<vector<vector<T> > >& vec);

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

template <typename A, typename B, typename C>
ostream& operator<<(ostream& os, const tuple<A, B, C>& t) {
    const auto& [a, b, c] = t;
    return os << "(" << a << ", " << b << ", " << c << ")";
}

template <typename A, typename B, typename C, typename D>
ostream& operator<<(ostream& os, const tuple<A, B, C, D>& t) {
    const auto& [a, b, c, d] = t;
    return os << "(" << a << ", " << b << ", " << c << ", " << d << ")";
}

template <typename T>
ostream& operator<<(ostream& os, priority_queue<T> pq) {
    os << "{";
    while (!pq.empty()) os << pq.top() << (pq.size() > 1 ? " " : ""), pq.pop();
    return os << "}";
}

#define FOREACH(it, a) for (auto it = (a).begin(); it != (a).end(); it++)

template <typename T>
ostream& operator<<(ostream& os, const set<T>& se) {
    os << "{";
    FOREACH (it, se) { os << (it == se.begin() ? "" : " ") << *it; }
    return os << "}";
}

template <typename T>
ostream& operator<<(ostream& os, const multiset<T>& ms) {
    os << "{";
    FOREACH (it, ms) { os << (it == ms.begin() ? "" : " ") << *it; }
    return os << "}";
}

template <typename T, typename U>
ostream& operator<<(ostream& os, const map<T, U>& ma) {
    os << "{";
    FOREACH (it, ma) { os << (it == ma.begin() ? "" : " ") << *it; }
    return os << "}";
}

template <typename T>
ostream& operator<<(ostream& os, const vector<T>& vec) {
    os << "{";
    FOREACH (it, vec) { os << (it == vec.begin() ? "" : " ") << *it; }
    return os << "}";
}

template <typename T>
ostream& operator<<(ostream& os, const vector<vector<T> >& vec) {
    os << "{\n";
    FOREACH (it, vec) { os << (it == vec.begin() ? " " : "\n ") << *it; }
    return os << "\n}";
}

template <typename T>
ostream& operator<<(ostream& os, const vector<vector<vector<T> > >& vec) {
    os << "{\n";
    FOREACH (it, vec) {
        os << (it == vec.begin() ? "" : "\n") << "(" << it - vec.begin() << ") " << *it;
    }
    return os << "\n}";
}

void dump() {}
template <typename Head, typename... Tail>
void dump(const Head& head, const Tail&... tail) {
    cout << head << (sizeof...(tail) ? ", " : "\n"), dump(tail...);
}

#ifdef _DEBUG
#define DUMP(...) cout << "[" << (#__VA_ARGS__) << "] ", dump(__VA_ARGS__)
#else
#define DUMP(...) (void)0
#endif

#endif