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 biggestSum = 0;
        
        
        int currLen = 2;
        for(int k = 0; k < A.length; k++) {
            long sum = 0;
            for(int i=0; i < currLen - 1; i++) {
                for(int j= i + 1; j < currLen - 1; j++) {
                    sum = sum + (A[i] * A[j]);
                }
            }
            biggestSum = Math.max(biggestSum, sum);
            currLen++;
        }
        
        return biggestSum;
        
    }

    private static class Pair {
        
        int left;
        int right;
        
        Pair(int left, int right) {
            this.left = left;
            this.right = right;
        }
        
        long getSum() {
            return left * right;
        }
    }
    
    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();
    }
}