output_description: Assume that there are K strings of length N that are in normal form: w_1,
  \ldots, w_K in lexicographical order. Output should be in the following
  format:
  
      
      
      w_1
      :
      w_K
      
  
  * * *
input_description: Input is given from Standard Input in the following format:
  
      
      
      N
attempt: N = int(input().rstrip())
  zumi = []
  for i in range(1, N + 1):
      ret = "a" * i + "b" * (N - i)
      # print(f'origin: {ret}')
      for j in range(i, N + 1):
          # print(f'1: {ret[:j-1]}, 2: {ret[j:]}')
          tmp = ret[: j - 1] + "a" + ret[j:]
          if tmp not in zumi:
              zumi.append(tmp)
  for x in sorted(zumi):
      print(x)
  
problem_description: Statement
  
  In this problem, we only consider strings consisting of lowercase English
  letters.
  
  Strings s and t are said to be **isomorphic** when the following conditions
  are satisfied:
  
    * |s| = |t| holds.
    * For every pair i, j, one of the following holds:
      * s_i = s_j and t_i = t_j.
      * s_i \neq s_j and t_i \neq t_j.
  
  For example, `abcac` and `zyxzx` are isomorphic, while `abcac` and `ppppp` are
  not.
  
  A string s is said to be in **normal form** when the following condition is
  satisfied:
  
    * For every string t that is isomorphic to s, s \leq t holds. Here \leq denotes lexicographic comparison.
  
  For example, `abcac` is in normal form, but `zyxzx` is not since it is
  isomorphic to `abcac`, which is lexicographically smaller than `zyxzx`.
  
  You are given an integer N. Print all strings of length N that are in normal
  form, in lexicographically ascending order.
samples: [{"input": "1", "output": "a\n    \n\n* * *"}, {"input": "2", "output": "aa\n    ab"}]