## https://yukicoder.me/problems/no/1564

def main():
    N = int(input())
    A = list(map(int, input().split()))

    A.sort()
    answer = 0
    for i in range(N):
        a = A[2 * i]
        b = A[2 * i + 1]
        answer += a * b
    print(answer)

if __name__ == '__main__':
    main()