n = int(input())
l = [int(i) for i in input().split(" ")]
ans = -1
for i in range(n):
    for j in range(i + 1, n):
        m = l[i:j + 1]
        #print(m)
        t = 0
        for x in range(len(m)-1):
            for y in range(x + 1, len(m)):
                #print(m[x],m[y])
                t += m[x]*m[y]
        ans = max(ans, t)
print(ans)