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 = list(input())
  for i in range(n):
      S[i] = ord(S[i]) - 97
  T = S[::-1]
  U = S + T
  f = 0
  for i in range(26):
      A = []
      for j in range(2 * n):
          if U[j] == i:
              f = 1
              A.append(j)
      if f == 1:
          c = i
          break
  B = []
  for i in range(1, len(A)):
      a = 1
      if A[i] == A[i - 1] + 1:
          a = a + 1
          if A[i] >= n:
              B.append([a, A[i]])
      else:
          a = 1
          if A[i] >= n:
              B.append([a, A[i]])
  C = []
  b = max(B[i][0] for i in range(len(B)))
  for i in range(len(B)):
      if B[i][0] == b:
          C.append(B[i][1])
  if b * 2 ** (k - 1) >= n:
      for i in range(n):
          print(chr(97 + c), end="")
      print()
      exit()
  Ans = []
  d = n - b * 2 ** (k - 1)
  for i in range(len(C)):
      AAns = U[C[i] - d - 1 : C[i] - 1]
      Ans.append(AAns[::-1])
  Ans.sort()
  for i in range(b * 2 ** (k - 1)):
      print(chr(97 + c), end="")
  for i in range(n - b * 2 ** (k - 1)):
      print(chr(97 + Ans[0][i]), end="")
  print()
  
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"}]