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())
  if N == 1:
      for i0 in range(1):
          print(chr(i0 + 97), sep="")
  if N == 2:
      for i0 in range(1):
          for i1 in range(i0 + 2):
              print(chr(i0 + 97), chr(i1 + 97), sep="")
  if N == 3:
      for i0 in range(1):
          for i1 in range(i0 + 2):
              for i2 in range(max(i0, i1) + 2):
                  print(chr(i0 + 97), chr(i1 + 97), chr(i2 + 97), sep="")
  if N == 4:
      for i0 in range(1):
          for i1 in range(i0 + 2):
              for i2 in range(max(i0, i1) + 2):
                  for i3 in range(max(i0, i1, i2) + 2):
                      print(
                          chr(i0 + 97), chr(i1 + 97), chr(i2 + 97), chr(i3 + 97), sep=""
                      )
  if N == 5:
      for i0 in range(1):
          for i1 in range(i0 + 2):
              for i2 in range(max(i0, i1) + 2):
                  for i3 in range(max(i0, i1, i2) + 2):
                      for i4 in range(max(i0, i1, i2, i3) + 2):
                          print(
                              chr(i0 + 97),
                              chr(i1 + 97),
                              chr(i2 + 97),
                              chr(i3 + 97),
                              chr(i4 + 97),
                              sep="",
                          )
  if N == 6:
      for i0 in range(1):
          for i1 in range(i0 + 2):
              for i2 in range(max(i0, i1) + 2):
                  for i3 in range(max(i0, i1, i2) + 2):
                      for i4 in range(max(i0, i1, i2, i3) + 2):
                          for i5 in range(max(i0, i1, i2, i3, i4) + 2):
                              print(
                                  chr(i0 + 97),
                                  chr(i1 + 97),
                                  chr(i2 + 97),
                                  chr(i3 + 97),
                                  chr(i4 + 97),
                                  chr(i5 + 97),
                                  sep="",
                              )
  if N == 7:
      for i0 in range(1):
          for i1 in range(i0 + 2):
              for i2 in range(max(i0, i1) + 2):
                  for i3 in range(max(i0, i1, i2) + 2):
                      for i4 in range(max(i0, i1, i2, i3) + 2):
                          for i5 in range(max(i0, i1, i2, i3, i4) + 2):
                              for i6 in range(max(i0, i1, i2, i3, i4, i5) + 2):
                                  print(
                                      chr(i0 + 97),
                                      chr(i1 + 97),
                                      chr(i2 + 97),
                                      chr(i3 + 97),
                                      chr(i4 + 97),
                                      chr(i5 + 97),
                                      chr(i6 + 97),
                                      sep="",
                                  )
  if N == 8:
      for i0 in range(1):
          for i1 in range(i0 + 2):
              for i2 in range(max(i0, i1) + 2):
                  for i3 in range(max(i0, i1, i2) + 2):
                      for i4 in range(max(i0, i1, i2, i3) + 2):
                          for i5 in range(max(i0, i1, i2, i3, i4) + 2):
                              for i6 in range(max(i0, i1, i2, i3, i4, i5) + 2):
                                  for i7 in range(max(i0, i1, i2, i3, i4, i5, i6) + 2):
                                      print(
                                          chr(i0 + 97),
                                          chr(i1 + 97),
                                          chr(i2 + 97),
                                          chr(i3 + 97),
                                          chr(i4 + 97),
                                          chr(i5 + 97),
                                          chr(i6 + 97),
                                          chr(i7 + 97),
                                          sep="",
                                      )
  if N == 9:
      for i0 in range(1):
          for i1 in range(i0 + 2):
              for i2 in range(max(i0, i1) + 2):
                  for i3 in range(max(i0, i1, i2) + 2):
                      for i4 in range(max(i0, i1, i2, i3) + 2):
                          for i5 in range(max(i0, i1, i2, i3, i4) + 2):
                              for i6 in range(max(i0, i1, i2, i3, i4, i5) + 2):
                                  for i7 in range(max(i0, i1, i2, i3, i4, i5, i6) + 2):
                                      for i8 in range(
                                          max(i0, i1, i2, i3, i4, i5, i6, i7) + 2
                                      ):
                                          print(
                                              chr(i0 + 97),
                                              chr(i1 + 97),
                                              chr(i2 + 97),
                                              chr(i3 + 97),
                                              chr(i4 + 97),
                                              chr(i5 + 97),
                                              chr(i6 + 97),
                                              chr(i7 + 97),
                                              chr(i8 + 97),
                                              sep="",
                                          )
  if N == 10:
      for i0 in range(1):
          for i1 in range(i0 + 2):
              for i2 in range(max(i0, i1) + 2):
                  for i3 in range(max(i0, i1, i2) + 2):
                      for i4 in range(max(i0, i1, i2, i3) + 2):
                          for i5 in range(max(i0, i1, i2, i3, i4) + 2):
                              for i6 in range(max(i0, i1, i2, i3, i4, i5) + 2):
                                  for i7 in range(max(i0, i1, i2, i3, i4, i5, i6) + 2):
                                      for i8 in range(
                                          max(i0, i1, i2, i3, i4, i5, i6, i7) + 2
                                      ):
                                          for i9 in range(
                                              max(i0, i1, i2, i3, i4, i5, i6, i7, i8) + 2
                                          ):
                                              print(
                                                  chr(i0 + 97),
                                                  chr(i1 + 97),
                                                  chr(i2 + 97),
                                                  chr(i3 + 97),
                                                  chr(i4 + 97),
                                                  chr(i5 + 97),
                                                  chr(i6 + 97),
                                                  chr(i7 + 97),
                                                  chr(i8 + 97),
                                                  chr(i9 + 97),
                                                  sep="",
                                              )
  
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"}]