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 n) {
        // Return the largest value of any of A's nonempty subarrays.
        int c=0;
        for(int i =0;i<n;i++)
        {   int j=0;
         while(j!=n)
         { j++;
            if(A[i]==A[j]||A[i]+A[j]==0)
            {
                A[i]=A[j+1];c++;
                
            }}n=n-c;
        }int sum=0;
        for(int i =0;i<n;i++)
        { int j=i+1;
         while(j!=n+1)
         { int product=A[i]*A[j];
          sum=sum+product;}
         }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,n);
        System.out.println(result);
        in.close();
    }
}