#!/bin/python3

import sys

def largestValue(ar):
    
    def prefsum(xs):
        out = [0]
        for x in xs:
            out.append(out[-1] + x)
        return(out)
    
    def pairsum2(xs):
        s = sum(xs)
        squares = sum(x ** 2 for x in xs)
        return (s ** 2 - squares) // 2
    
    # Return the largest value of any of A's nonempty subarrays.
    n = len(ar)
    from math import inf
    max_val = -inf
    
    sums = prefsum(ar)
    squares = prefsum([x ** 2 for x in ar])
    #print(sums)
    #print(squares)
    
    for start in range(n - 1):
        for end in range(start + 2, n + 1):
            cur = (sums[end] - sums[start]) ** 2 - (squares[end] - squares[start])
            max_val = max(max_val, cur // 2)
            
    return max_val

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