output_description: Print the lexicographically smallest string that Iroha can produce.
  
  * * *
input_description: The input is given from Standard Input in the following format:
  
      
      
      N L
      S_1
      S_2
      :
      S_N
attempt: N, L = map(int, input().split())
   
  #標準入力からリストの作成
  list = []
  for _ in range(1,N):
   i = input()
   list.append(i)
   
  #リストの結合
  mojiretu = ''.join(list)
   
  print(mojiretu
problem_description: Statement
  
  Iroha has a sequence of N strings S_1, S_2, ..., S_N. The length of each
  string is L.
  
  She will concatenate all of the strings in some order, to produce a long
  string.
  
  Among all strings that she can produce in this way, find the lexicographically
  smallest one.
  
  Here, a string s=s_1s_2s_3...s_n is _lexicographically smaller_ than another
  string t=t_1t_2t_3...t_m if and only if one of the following holds:
  
    * There exists an index i(1≦i≦min(n,m)), such that s_j = t_j for all indices j(1≦j<i), and s_i<t_i.
    * s_i = t_i for all integers i(1≦i≦min(n,m)), and n<m.
samples: [{"input": "3 3\n    dxx\n    axx\n    cxx", "output": "axxcxxdxx\n    \n\nThe following order should be used: `axx`, `cxx`, `dxx`."}]