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

int main() {
  int N;
  int64_t sum = 0;
  cin >> N;
  vector<int> A(N * 2);
  for (int &a : A) cin >> a;
  sort(A.begin(), A.end());

  for (int i = 0; i < N * 2 - 1; i += 2)
    sum += (int64_t)A.at(i) * A.at(i + 1);
  cout << sum << endl;
}