import java.io.*;
import java.util.*;
import java.text.*;
import java.math.*;
import java.util.regex.*;

public class Solution {

    static long largestValue(int[] a) {
        Arrays.sort(a);
        int length = a.length;
        int sum = 0;
        for (int i = 1; i < length; i++) {
            for (int j = i + 1; j < length; j++) {
                sum += a[i] * a[j];
            }
        }
        return sum;
    }

    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int n = in.nextInt();
        int[] A = new int[n];
        for(int A_i = 0; A_i < n; A_i++){
            A[A_i] = in.nextInt();
        }
        long result = largestValue(A);
        System.out.println(result);
        in.close();
    }
}