#!/bin/python3

import sys
from itertools import *
def vu(x):
    k=list(combinations(x,2))
    v=sum(list(map(lambda x:x[0]*x[1],k)))
    return v


def largestValue(A):
   
    b=list(combinations(A,(n//2)+1))
    b=[vu(i) for i in b]
    return max(b)

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