import java.util.*;

public class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    int number_n = Integer.parseInt(sc.next());
    int number_k = Integer.parseInt(sc.next());
    String str = sc.next();
    if(number_k == 1) str = str.substring(0, 1).toLowerCase() + str.substring(1);
    else str = str.substring(0, number_k - 1) + str.substring(number_k - 1, number_k).toLowerCase() + str.substring(number_k);
    System.out.println(str);
  }
}

/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