output_description: Print the string S after lowercasing the K-th character in it.
  
  * * *
input_description: Input is given from Standard Input in the following format:
  
      
      
      N K
      S
attempt: icase = 0
  if icase == 0:
      n, k = map(int, input().split())
      s = input()
      if k == 1:
          s1 = ""
          s2 = s[0]
          s3 = s[1:]
      elif k == n:
          s1 = s[: n - 1]
          s2 = s[n - 1]
          s3 = ""
      else:
          s1 = s[: k - 1]
          s2 = s[k - 1]
          s3 = s[k:]
      if s2 == "A":
          s2 = "a"
      elif s2 == "B":
          s2 = "b"
      elif s2 == "C":
          s2 = "c"
      print(s1 + s2 + s3)
  
problem_description: Statement
  
  You are given a string S of length N consisting of `A`, `B` and `C`, and an
  integer K which is between 1 and N (inclusive). Print the string S after
  lowercasing the K-th character in it.
samples: [{"input": "3 1\n    ABC", "output": "aBC\n    \n\n* * *"}, {"input": "4 3\n    CABA", "output": "CAbA"}]