#!/bin/python

import sys

def find_value(a):

    if len(a) == 0:
        return 0

    if len(a) == 1:
        return 1

    if len(a) == 2:
        return a[0]*a[1]

    res = 0

    for x in range(len(a)):
        for y in range(len(a)):
            if x==y:
                continue
            else:
                res += a[x]*a[y]

    return res/2

def largestValue(A):

    b = A
    x = A

    b.pop(0)
    x.pop(-1)

    res = find_value(b)
    rest = find_value(x)

    if res > rest:
        b = b
        res = res
    else:
        b = x
        res = rest

    while(True):

        c = b
        d = b
        c.pop(0)
        d.pop(-1)

        res1 = find_value(c)
        res2 = find_value(d)

        if res1 > res:
            b = c
            res = res1
        if res2 > res:
            d = c
            res = res2

        if res > res1 and res > res2:
            break

    return res

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