using System;

public class Hello
{
    static void Main()
    {
        var n = int.Parse(Console.ReadLine().Trim());
        string[] line = Console.ReadLine().Trim().Split(' ');
        var a = Array.ConvertAll(line, long.Parse);
        getAns(n, a);
    }
    static void getAns(int n, long[] a)
    {
        n *= 2;
        var ans = 0L;
        Array.Sort(a);
        for (int i = 0; i < n; i += 2)
            ans += a[i] * a[i + 1];
        Console.WriteLine(ans);
    }
}