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: a = int(input())
  b = [1] * a
  c = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
  d = 0
  core = c[0:a]
  print("a" * a)
  while b != core:
      b[-1] = b[-1] + 1
  for i in range(10):
      if b[-i - 1] - 1 > b[-i - 2]:
          b[-i - 2] = b[-i - 2] + 1
          b[-i - 1] = 1
      else:
          break
  answer = ""
  for j in range(a):
      answer = answer + chr(b[j] + 96)
  print(answer)
  
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"}]