//#include <atcoder/all>
#include<bits/stdc++.h>
using namespace std;
//using namespace atcoder;
using ll = long long;
#define all(A) A.begin(),A.end()
using vll = vector<ll>;
#define rep(i, n) for (long long i = 0; i < (long long)(n); i++)
using Graph = vector<vector<pair<ll, ll>>>;
vector<ll> fact, factinv, inv;
ll mod = 998244353;
ll gcd(ll(a), ll(b)) {
	ll c = a;
	while (a % b != 0) {
		c = a % b;
		a = b;
		b = c;
	}
	return b;
}

int main() {
   ll N;
   cin>>N;
   vll A(2*N);
   rep(i,2*N)cin>>A[i];
   sort(all(A));
   ll an=0;
   rep(i,N){
       an+=A[i*2]*A[i*2+1];
   }
   cout<<an<<endl;
}