#include <bits/stdc++.h>
using namespace std;
using ll = long long;

#define REP(i, n) for(int i=0;i<(int)(n);i++)

int main() {
    int N;
    cin >> N;
    vector<int> a(2*N);
    REP(i, 2*N) cin >> a[i];
    sort(a.rbegin(), a.rend());
    ll ans = 0;
    for(int i = 0 ; i < 2*N; i += 2) ans += (ll)a[i] * a[i+1];
    cout << ans << endl;
}