output_description: If store A is closer, print `A`; if store B is closer, print `B`.
  
  * * *
input_description: Input is given from Standard Input in the following format:
  
      
      
      x a b
attempt: S = list(input())
  
  # 重要：アルファベットの配列を生成
  alphabets = [chr(ord('a') + i) for i in range(26)]
  
  # 除外文字を配列に入れる
  excludeS = []
  for i in range(len(alphabets)):
      if alphabets[i] not in S:
          excludeS.append(alphabets[i])
          flag = False
          if alphabets[i] == 'Z'
              flag = True
      else:
          flag = True
  
  if flag:
      print('None')
  else:
      # 辞書順に並び変えて一番小さい文字を求める
      sortedExcludeS = sorted(excludeS)
      minExcludeS = min(sortedExcludeS)
      print(minExcludeS)
  
problem_description: Statement
  
  Snuke lives at position x on a number line. On this line, there are two stores
  A and B, respectively at position a and b, that offer food for delivery.
  
  Snuke decided to get food delivery from the closer of stores A and B. Find out
  which store is closer to Snuke's residence.
  
  Here, the distance between two points s and t on a number line is represented
  by |s-t|.
samples: [{"input": "5 2 7", "output": "B\n    \n\nThe distances between Snuke's residence and stores A and B are 3 and 2,\nrespectively. Since store B is closer, print `B`.\n\n* * *"}, {"input": "1 999 1000", "output": "A"}]