#!/bin/python3

import sys
from itertools import combinations

def largestValue(A):
    # Return the largest value of any of A's nonempty subarrays.
    x=set(A)
    x=list(x)
    (j,i,ans)=(0,0,0)
    l= (len(x))
    for i in range(0,l):
        for j in range(i+1,l-1):
            if (abs(x[i])==abs(x[j])):
                 del x[j]
    #print (x)
    perm = list(combinations(x, 2))
    lp=len(perm)
   # print (perm)
    for i in range(lp):
        ans=ans+ ((perm[i][0])*perm[i][1])
    return (ans)
if __name__ == "__main__":
    n = int(input().strip())
    A = list(map(int, input().strip().split(' ')))
    result = largestValue(A)
    print(result)