output_description: Print the lexicographically smallest possible string that can be the string S
  after the K operations.
  
  * * *
input_description: Input is given from Standard Input in the following format:
  
      
      
      N K
      S
attempt: N, K = map(int, input().split())
  S = input()
  T = S[::-1]  # 文字列反転
  U = S + T
  D = []
  for i in range(N):
      D.append(U[i : i + N])
  D.sort()
  B = D[0]
  for i in range(N):
      if B[i] != B[0]:
          break
  if i * 1 << (K - 1) > N:
      print(B[0] * N)
  else:
      print((B[0] * (i * (1 << (K - 1))) + B[i:])[:N])
  
problem_description: Statement
  
  Takahashi has a string S of length N consisting of lowercase English letters.
  On this string, he will perform the following operation K times:
  
    * Let T be the string obtained by reversing S, and U be the string obtained by concatenating S and T in this order.
    * Let S' be some contiguous substring of U with length N, and replace S with S'.
  
  Among the strings that can be the string S after the K operations, find the
  lexicographically smallest possible one.
samples: [{"input": "5 1\n    bacba", "output": "aabca\n    \n\nWhen S=`bacba`, T=`abcab`, U=`bacbaabcab`, and the optimal choice of S' is\nS'=`aabca`.\n\n* * *"}, {"input": "10 2\n    bbaabbbaab", "output": "aaaabbaabb"}]