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: from heapq import *
  
  N = int(input())
  a = list(map(int, input().split()))
  
  sumS1 = [0 for i in range(N + 1)]
  S1 = a[0:N]
  heapify(S1)
  sumS1[0] = sum(S1)
  
  for k in range(1, N + 1):
      if S1[0] < a[N + k - 1]:
          sumS1[k] = sumS1[k - 1] + a[N + k - 1] - S1[0]
          heapreplace(S1, a[N + k - 1])
      else:
          sumS1[k] = sumS1[k - 1]
  
  sumS2 = [0 for i in range(N + 1)]
  S2 = [-1 * i for i in a[2 * N : 3 * N]]
  heapify(S2)
  sumS2[N] = sum(S2)
  
  for k in range(1, N + 1):
      if S2[0] < -1 * a[2 * N - k]:
          sumS2[N - k] = sumS2[N - k + 1] - a[2 * N - k] - S2[0]
          heapreplace(S2, -1 * a[2 * N - k])
      else:
          sumS2[N - k] = sumS2[N - k + 1]
  
  
  res = [float("-inf")] * (N + 1)
  for i in range(N + 1):
      res[i] = sumS1[i] + sumS2[i]
  
  res.sort()
  print(res[N])
  
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."}]