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

public class Solution {

    static long largestValue(int[] A,int len) {
        int i,j,k,flag=0,sum=0,n;    
        Arrays.sort(A);
        for(i=0;i<len;i++){
            if(A[i]>=0)
                break;
        }
        n=len-i-1;
        for(i=i-1;i<len;i++)
        {
            for(j=i+1;j<len;j++){
                sum+=A[i]*A[j];
                //System.out.println(A[i]+"*"+A[j]);
            }
        }
        return sum;
        // Return the largest value of any of A's nonempty subarrays.
    }

    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,n);
        System.out.println(result);
        in.close();
    }
}