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: n = int(input())
  ds = list(map(int, input().split()))
  
  from collections import defaultdict
  d = defaultdict(int)
  
  d[0] = 1
  for d_ in ds:
      d[d_] += 1
      if d_ == 12 and d[d_] == 2:
          print(0)
          exit()
      elif d_ == 0 and d[d_] == 2: 
          print(0)
          exit()
      elif d[d_] == 3:
          print(0)
          exit()
  
  def calcmin(tmp):
      n = len(tmp)
      ret = 1 << 50
      for i in range(n):
          for j in range(i+1,n):
              ret = min(ret, abs(tmp[i]-tmp[j]))
      return ret
  
  two = []
  x = []
  for k in d.keys():
      if d[k] == 2:
          two.append(k)
          two.append(24-k)
      if d[k] == 1:
          x.append(k)
  two = list(set(two))
  n = len(x)
  
  ans = 0
  for i in range(1 << n):
      tmp[] = x[:]
      for j in range(n):
          if i & (1 << j):
              tmp[j] = 24-x[j]
      tmp.extend(two)
      ans = max(calcmin(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."}]