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 itertools import product
  from collections import Counter
  
  
  def main():
      N, *D = map(int, open(0).read().split())
      C = Counter(D)
      ans = min(D)
      for i in range(1, 12):
          if i in C and C[i] >= 3:
              ans = 0
      if 12 in C and C[12] >= 2:
          ans = 0
      if ans:
          X1 = [k for k, v in C.items() if v == 1]
          X2 = [k for k, v in C.items() if v == 2]
          Y = [False] * 24
          for x in X2:
              Y[x] = Y[-x] = True
          res = 0
          for p in product((True, False), repeat=len(X1)):
              Z = Y.copy()
              for t, x in zip(p, X1):
                  if t:
                      Z[x] = True
                  else:
                      Z[-x] = True
              res2 = 12
              I = [i for i, p in enumerate(Z) if p]
              for i in I:
                  for j in I:
                      if i == j:
                          continue
                      res2 = min(res2, abs(i - j))
              res = max(res, res2)
          ans = min(ans, res)
      print(ans)
  
  
  if __name__ == "__main__":
      main()
  
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."}]