#!/bin/python3

import sys
def computevalue(a):
    n=len(a)
    sum1=0
    for i in range(n):
        for j in range(i+1,n):
            sum1+=a[i]*a[j]
    return sum1
def largestValue(A):
    max1=0
    for i in range(n):
        for j in range(n,i+1,-1):
            temp=computevalue(A[i:j])
            if temp>max1:
                max1=temp
    return max1
    # Return the largest value of any of A's nonempty subarrays.

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