import sys
#sys.setrecursionlimit(10 ** 6)
INF = float('inf')
#10**20に変えるのもあり
MOD = 10**9 + 7
MOD2 = 998244353
def solve():
    def II(): return int(sys.stdin.readline())
    def LI(): return list(map(int, sys.stdin.readline().split()))
    def LC(): return list(input())
    def IC(): return [int(c) for c in input()]
    def MI(): return map(int, sys.stdin.readline().split())
    N=II()
    A = LI()
    A.sort(reverse = True)
    Ans = 0
    #print(A)
    for k in range(N):
        #print(A[2*k+1],A[2*k])
        Ans += A[2*k+1]*A[2*k]
    print(Ans)
    return
solve()