#!/bin/python3

import sys

def largestValue(a):
    # Return the largest value of any of A's nonempty subarrays.
    a.sort(reverse=True)
    #print(a)
    s=a[:4]
    #print(s)
    #q=itertools.combinations(s,2)
    #print(q)
    su=0
    for i in range(len(s)-1):
    	for j in range(i+1,len(s)):
    		su+=(s[i]*s[j])

    return su



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