#include <bits/stdc++.h>
#define rep(i, n) for (int i = 0; i < n; ++i)
typedef long long ll;
using namespace std;

int main() {
    int N;
    cin >> N;
    vector<ll> A(N * 2);
    rep(i, N * 2) cin >> A[i];

    sort(A.rbegin(), A.rend());

    ll ans = 0;
    for (int i = 1; i < N * 2; i += 2) {
        ans += A[i] * A[i - 1];
    }
    cout << ans << endl;

    return 0;
}