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

public class Solution {

    public static void main(String[] args) {
       Scanner input = new Scanner(System.in);
		Integer n = input.nextInt();
		int[] array = new int[n];
		int temp;
		//int[] revArray = new int[n];
		for(int i=0;i<n;i++) {
			array[i] = input.nextInt();
		}
		int sum=0;
		for (int i = 0; i < n; i++) 
        {
            for (int j = i + 1; j < n; j++) 
            {
                if (array[i] < array[j]) 
                {
                    temp = array[i];
                    array[i] = array[j];
                    array[j] = temp;
                }
            }
        }
		for(int k=0;k<3;k++) {
			for(int l=k+1;l<4;l++) {
				sum = sum + array[k] * array[l];
				
			}
		}
		System.out.println(sum);
	}
}