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()
  
  lex_min = "z"
  for char in S:
      lex_min = min(char, lex_min)
  
  if (1 << (K - 1)) > N:
      print(lex_min * N)
  else:
      U = S + S[::-1]
      candidates = []
      for i in range(N, N << 1):
          if U[i] == lex_min:
              M = U[i - N + 1 : i + 1]
              if K > 1:
                  candidates.append((1 << (K - 1)) * lex_min + M[: N - (1 << (K - 1))])
              else:
                  candidates.append(M)
      print(min(candidates))
  
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"}]