def sub_lists(my_list):
	subs = [[]]
	for i in range(len(my_list)):
		n = i+1
		while n <= len(my_list):
			sub = my_list[i:n]
			subs.append(sub)
			n += 1
	
	return subs

n = int(input().strip())
A = list(map(int, input().strip().split(' ')))
B = sub_lists(A)
max_sum = -10**9
for i in B:
    s = 0
    for j in range(len(i)):
        for k in range(j+1,len(i)):
            s += i[j]*i[k]
    if s > max_sum:
        max_sum = s
print(max_sum)