import java.util.*;
 
public class Main{
  public static void main(String[] args) {
    Scanner scanner = new Scanner(System.in);
    String nk = scanner.nextLine();
    String s = scanner.nextLine();
    int toLowerCaseIdx = Integer.parseInt(nk.split(" ")[1]);
    StringBuilder sb = new StringBuilder(s);
    sb.replace(toLowerCaseIdx-1,toLowerCaseIdx,s.substring(toLowerCaseIdx-1,toLowerCaseIdx).toLowerCase());
    System.out.println(sb);
  }
}
/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