#include <iostream>
#include <vector>
#include <map>
#include <algorithm>
#include <functional>

using namespace std;

int main() {
  int n;
  cin >> n;
  vector<long long> a(2 * n);
  for (int i = 0; i < 2 * n; i++) {
    cin >> a[i];
  }
  sort(a.begin() , a.end());
  long long b = 0;
  for (int i = 0; i < a.size() - 1; i += 2) {
    long long now = a[i] * a[i + 1];
    //cout << now << endl;
    b += now;
  }
  cout << b << endl;
  return 0;
}