#!/bin/python3

import sys

def valueOf(A):
    result = 0
    for i in range(len(A)-1):
        for j in range(i + 1, len(A)):
            result += A[i]*A[j]
    return result

def largestValue(A):
    maxVal = None
    for length in range(1, len(A)+1):
        for i in range(len(A) - length + 1):
            val = valueOf(A[i:i+length])
            if maxVal == None or val > maxVal:
                maxVal = val
    return maxVal

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