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: import heapq
  
  N = int(input())
  a = list(map(int, input().split()))
  # print(a)
  b = a[::-1]
  A = a[:N]
  # print(A)
  AR = [A[0]]
  for i in range(1, len(A) * 2):
      AR.append(a[i] + AR[i - 1])
  # print("AR",AR)
  AL = []
  
  heapq.heapify(A)
  for i in range(N, N * 2):
      heapq.heappush(A, a[i])
      AL.append(A[0])
      heapq.heappop(A)
  # print(AL)
  ALR = [AL[0]]
  for i in range(1, len(AL)):
      ALR.append(ALR[i - 1] + AL[i])
  # print(ALR)
  ANSA = [AR[N - 1]]
  for i in range(len(ALR)):
      ANSA.append(AR[N + i] - ALR[i])
  # print(ANSA)
  
  B = b[:N]
  for i in range(len(B)):
      B[i] *= -1
  # print("B",B)
  BR = [B[0]]
  for i in range(1, len(B) * 2):
      BR.append(-b[i] + BR[i - 1])
  # print("BR",BR)
  BL = []
  # print("B",B)
  heapq.heapify(B)
  for i in range(N, N * 2):
      heapq.heappush(B, -b[i])
      BL.append(-B[0])
      heapq.heappop(B)
  # print("BL",BL)
  BLR = [BL[0]]
  for i in range(1, len(BL)):
      BLR.append(BLR[i - 1] + BL[i])
  # print("BLR",BLR)
  BNSA = [BR[N - 1]]
  for i in range(len(BLR)):
      BNSA.append(BR[N + i] + BLR[i])
  # print(BNSA)
  BNSA = BNSA[::-1]
  # print(BNSA)
  ANS = -(10**20)
  for i in range(len(BNSA)):
      if (ANSA[i] + BNSA[i]) > ANS:
          ANS = ANSA[i] + BNSA[i]
  print(ANS)
  
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."}]