#!/bin/python3

import sys

def largestValue(A):
    # Return the largest value of any of A's nonempty subarrays.
    A.sort()
    for i in range(0,len(A)):
        if A[i]>=0:
            sub_arr=A[i-1:]
            break
    i=0
    su=0
    while i < len(sub_arr):
        j=i+1
        while j < len(sub_arr):
            su=su+sub_arr[i]*sub_arr[j]    
            j=j+1
        i=i+1      
    return su

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