#include <bits/stdc++.h>
using namespace std;
int main(){
  int N;
  cin >> N;
  vector<int> A(N * 2);
  for (int i = 0; i < N * 2; i++){
    cin >> A[i];
  }
  sort(A.begin(), A.end());
  long long ans = 0;
  for (int i = 0; i < N * 2; i += 2){
    ans += (long long) A[i] * A[i + 1];
  }
  cout << ans << endl;
}