#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;

int main()
{
	int N;
	cin >> N;
	vector<int> A(2 * N);
	for(int i = 0;i < 2 * N;i++)
	{
		cin >> A[i];
	}
	sort(A.begin(),A.end());
	long long ans = 0;
	for(int i = 0;i < 2 * N;i += 2)
	{
		ans += (long long) A[i] * A[i + 1];
	}
	cout << ans << "\n";
}