import java.util.Scanner;

public class Main {

  public static void main(String[] args) {
    Scanner scan = new Scanner(System.in);
    String line = scan.nextLine();
    int max = Integer.parseInt(line.split(" ")[0]);
    int target =Integer.parseInt(line.split(" ")[1]);
    line = scan.nextLine();
    char ch = line.charAt(target-1);
    ch = (char) (ch + 0x20);
    System.out.print(line.substring(0, target-1)+ ch + line.substring(target,max) );

  }

}
/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