output_description: Print the maximum possible value of s.
  
  * * *
input_description: Input is given from Standard Input in the following format:
  
      
      
      N
      D_1 D_2 ... D_N
attempt: from collections import Counter
  
  N = int(input())
  now_time = []
  D = list(map(int, input().split()))
  c = Counter(D)
  candidate = []
  for num, amount in c.items():
      if num == 0:
          print(0)
          exit()
      if amount > 2:
          print(0)
          exit()
      if amount == 2:
          # 確定した時間
          now_time.append(num)
          now_time.append(24 - num)
      if amount == 1:
          candidate.append((num, 24 - num))  # 選択の余地がある時間
  ans = 0
  # 確定した時間に、選択の余地がある組を追加していく
  for mask in range(1 << len(candidate)):
      list_0_1 = []
      time_list = now_time.copy()  # 確定している時間
      for i in range(len(candidate)):
          list_0_1.append(int((mask >> i) & 1))
      for i, num in enumerate(list_0_1):
          time_list.append(candidate[i][num])
      # exit()
      tmp = 100
      for i in range(len(time_list)):
          for j in range(i + 1, len(time_list)):
              tmp = min(tmp, abs(time_list[i] - time_list[j]))
      ans = max(tmp, ans)
  
  
  print(ans)
  
problem_description: Statement
  
  In CODE FESTIVAL XXXX, there are N+1 participants from all over the world,
  including Takahashi.
  
  Takahashi checked and found that the _time gap_ (defined below) between the
  local times in his city and the i-th person's city was D_i hours. The time gap
  between two cities is defined as follows. For two cities A and B, if the local
  time in city B is d o'clock at the moment when the local time in city A is 0
  o'clock, then the time gap between these two cities is defined to be
  min(d,24-d) hours. Here, we are using 24-hour notation. That is, the local
  time in the i-th person's city is either d o'clock or 24-d o'clock at the
  moment when the local time in Takahashi's city is 0 o'clock, for example.
  
  Then, for each pair of two people chosen from the N+1 people, he wrote out the
  time gap between their cities. Let the smallest time gap among them be s
  hours.
  
  Find the maximum possible value of s.
samples: [{"input": "3\n    7 12 8", "output": "4\n    \n\nFor example, consider the situation where it is 7, 12 and 16 o'clock in each\nperson's city at the moment when it is 0 o'clock in Takahashi's city. In this\ncase, the time gap between the second and third persons' cities is 4 hours.\n\n* * *"}, {"input": "2\n    11 11", "output": "2\n    \n\n* * *"}, {"input": "1\n    0", "output": "0\n    \n\nNote that Takahashi himself is also a participant."}]