#include <bits/stdc++.h>
#include<iostream>
#include<map>
#include<vector>
#include <algorithm>
#include<math.h>
#include <iomanip>
#include<set>
#include <numeric>
#include<string>
using ll = long long;
using namespace std;


int main()
{
    ll n, sum1 = 0;
    cin >> n;
    vector<ll> a(2*n);
    for (int i = 0; i < 2 *n; i++) cin >> a[i];
    sort(a.begin(), a.end());
    for (int i = 0; i < n; i++){
        sum1 += a[2*i] * a[2*i+1];
    }
    cout << sum1 << endl;
}