/* -*- coding: utf-8 -*-
 *
 * 1564.cc:  No.1564 Sum of Products of Pairs - yukicoder
 */

#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<cmath>
#include<iostream>
#include<string>
#include<vector>
#include<map>
#include<set>
#include<stack>
#include<list>
#include<queue>
#include<deque>
#include<algorithm>
#include<numeric>
#include<utility>
#include<complex>
#include<functional>
 
using namespace std;

/* constant */

const int MAX_N = 100000;
const int MAX_N2 = MAX_N * 2;

/* typedef */

typedef long long ll;

/* global variables */

int as[MAX_N2];

/* subroutines */

/* main */

int main() {
  int n;
  scanf("%d", &n);
  int n2 = n * 2;

  for (int i = 0; i < n2; i++) scanf("%d", as + i);
  sort(as, as + n2);

  ll sum = 0;
  for (int i = 0; i < n2; i += 2) sum += (ll)as[i] * as[i + 1];

  printf("%lld\n", sum);
  return 0;
}