output_description: Print the maximum possible score of a'.
  
  * * *
input_description: Input is given from Standard Input in the following format:
  
      
      
      N
      a_1 a_2 ... a_{3N}
attempt: def d_3n_numbers(N, A):
      import heapq
  
      left = A[:N]
      heapq.heapify(left)
      # heappopはキューの最小値を取り出すが、rightからは最大値を取り出したいので-1を掛ける
      # 後にマイナスが付いているところは、それの帳尻を合わせている
      right = [-i for i in A[2 * N :]]
      heapq.heapify(right)
  
      # 最初、leftには数列の先頭N個が、rightには末尾N個が格納されている
      # 数列のN番目から2N番目まで順に、leftに格納して最小値を捨てることを繰り返す
      # 数列の2N番目からN番目まで順に、rightに格納して最大値を捨てることを繰り返す
      left_sum = [sum(left)]
      right_sum = [-sum(right)]
      for k in range(N, 2 * N):
          heapq.heappush(left, A[k])
          v = heapq.heappop(left)
          left_sum.append(left_sum[-1] + A[k] - v)
      for k in range(2 * N - 1, N - 1, -1):
          heapq.heappush(right, -A[k])
          v = heapq.heappop(right)
          right_sum.append(right_sum[-1] + A[k] - (-v))
  
      score = [a - b for a, b in zip(left_sum, right_sum[::-1])]
      return max(score)
  
  
  N = int(input())
  A = [int(i) for i in input().split()]
  print(d_3N_Numbers(N, A))
  
problem_description: Statement
  
  Let N be a positive integer.
  
  There is a numerical sequence of length 3N, a = (a_1, a_2, ..., a_{3N}). Snuke
  is constructing a new sequence of length 2N, a', by removing exactly N
  elements from a without changing the order of the remaining elements. Here,
  the score of a' is defined as follows: (the sum of the elements in the first
  half of a') - (the sum of the elements in the second half of a').
  
  Find the maximum possible score of a'.
samples: [{"input": "2\n    3 1 4 1 5 9", "output": "1\n    \n\nWhen a_2 and a_6 are removed, a' will be (3, 4, 1, 5), which has a score of (3\n+ 4) - (1 + 5) = 1.\n\n* * *"}, {"input": "1\n    1 2 3", "output": "-1\n    \n\nFor example, when a_1 are removed, a' will be (2, 3), which has a score of 2 -\n3 = -1.\n\n* * *"}, {"input": "3\n    8 2 2 7 4 6 5 3 8", "output": "5\n    \n\nFor example, when a_2, a_3 and a_9 are removed, a' will be (8, 7, 4, 6, 5, 3),\nwhich has a score of (8 + 7 + 4) - (6 + 5 + 3) = 5."}]