#include <bits/stdc++.h>

using namespace std;

int main() {
    int n;
    cin >> n;
    
    vector<int> a(2*n);
    for (auto &i: a) {
        cin >> i;
    }

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

    long long ans = 0;
    for (int i = 0; i < n; ++i) {
        ans += a[2*i] * a[2*i+1];
    }
    
    cout << ans << endl;
}