#!/bin/python3

import sys

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

def largestValue(A):
    # Return the largest value of any of A's nonempty subarrays.
    value_list = []
    for i in range(0, len(A)-1):
        for j in range(i+1, len(A)):
            value_list.append(value(A[i:j]))
    return(max(value_list))

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