#!/bin/python3

import sys

def largest(a):
    sum=0; 
    for i in range(len(a)-1):
        for j in range(i+1,len(a)):
            sum+= a[i]*a[j]
    return sum

def largestValue(A):
    # Return the largest value of any of A's nonempty subarrays.
    n = len(A); maxi = -sys.maxsize
    for i in range(n-1):
        for j in range(i+1, n):
            temp = A[i:j+1]
            #print(temp, largest(temp))
            maxi = max(maxi, largest(temp))
    return maxi

if __name__ == "__main__":
    n = int(input().strip())
    A = list(map(int, input().strip().split(' ')))
    result = largestValue(A)
    print(result)