import java.util.Scanner;
 
class Main {
  static Scanner sc = new Scanner(System.in);
    public static void main(String[] args) {
      
      int a = sc.nextInt();
      int b = sc.nextInt();
      String s = sc.next();
      char[] s_chars = s.toCharArray();
      s_chars[b-1]+=32;
      
      System.out.print(s_chars);
      

      
    }
}
/tmp/hf-datasets-cache/medium/datasets/42704881117311-config-parquet-and-info-qiankunmu-Project_CodeNet-896c9d36/hub/datasets--qiankunmu--Project_CodeNet_Python800_and_Java250/snapshots/c899fde44a77ba1cc14973ed3de064e4ff3aadc7/Project_CodeNet_Java250.tar.gz