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