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

public class Solution {

    static long largestValue(int[] A) {
        long max=0;int index=0,l=0;
        Arrays.sort(A);
        for(int i=0;i<A.length;i++)
        {
            if(index<A[i])
            {
               index = i-1;
                l=A[i];
                break;
            }
        }
        for(int i=index;i<=index+l;i++)
        {
            for(int j=i+1;j<=index+l;j++)
            max = max + (A[i]*A[j]);
        }
        return max;
    }

    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();
    }
}