#!/bin/python3

import sys

def pairWiseSum(arr):
    s = 0
    for ix, x in enumerate(arr):
        for iy, y in enumerate(arr):
            if ix > iy:
                s += arr[ix] * arr[iy]
    return s

def largestValue(A):
    # Return the largest value of any of A's nonempty subarrays.
    A = sorted(A)
    
    ret = A[0] * A[1] - 1
    
    for sidx in range(len(A)):
        for eidx in range(sidx+1, len(A)):
            ret = max(ret, pairWiseSum(A[sidx: eidx]))
     
    return ret
            

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