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