#include<bits/stdc++.h>
//#include <cmath>
using namespace std;
#define ll long long
#define rep(i,n) for(long long i = 0; i < (long long)(n); i++)
#define repi(i,a,b) for(long long i = (long long)(a);i < (long long)(b);i++)
template<class T>bool chmax(T &a, const T &b) { if (a<b) { a=b; return 1; } return 0; }
template<class T>bool chmin(T &a, const T &b) { if (b<a) { a=b; return 1; } return 0; }
#define pb push_back
#define fr first
#define sc second
#define ALL(x) (x).begin(),(x).end()
#define mod 998244353
#define MOD 1000000007
#define mp make_pair
#define P pair<int,int>
#define inf 1e9
const double pi=3.1415926535897932384626433832795028841971;
int main() {
  ll n;
  cin>>n;
  vector<ll> a(n*2);
  rep(i,n*2) cin>>a[i];
  sort(ALL(a));
  ll ans=0;
  rep(i,n){
    ans+=a[(i+1)*2-2]*a[(i+1)*2-1];
  }
  cout<<ans<<endl;
}