#!/bin/python3

import sys
def getSum(P):
    s = sum(P)
    s_s = sum([i*i for i in P])
    return (s*s-s_s)//2
def largestValue(A):
    # Return the largest value of any of A's nonempty subarrays.
    ans = 0
    for begin in range(len(A)):
        for end in range(2,len(A)):
            local = getSum(A[begin:end]);
            ans = max(ans,local)
    return ans
if __name__ == "__main__":
    n = int(input().strip())
    A = list(map(int, input().strip().split(' ')))
    result = largestValue(A)
    print(result)