#!/bin/python3

import sys
from itertools import combinations

def getvalue(arr):
    a = combinations(arr,2)
    l = list(map(lambda x: x[0]*x[1], a))
    return sum(l)

def largestValue(A):
    # Return the largest value of any of A's nonempty subarrays.
    res = set()
    for i in range(len(A)):
        myA = A[:i] + A[i+1:]
        res.add(getvalue(myA))
    return max(res)

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