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

public class Solution {

    static long largestValue(int[] A) {
        // Return the largest value of any of A's nonempty subarrays.
        long sum=0;
        long sum2=0;
        int count=0;
        for(int i=0;i<A.length-1;i++)
        {
            count=0;sum=0;
            for(int j=i+1;j<A.length;j++)
            {
                
                if(A[i]==A[j])
                {
                    A[j]=0;
                    count=1;
                    break;
                }
                sum+=A[i]*A[j];
            }
            if(count!=1)
            sum2+=sum;
        }
        
        return sum2;
    }

    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();
    }
}