import java.util.Scanner;
import java.util.List;
import java.util.ArrayList;
import java.util.Objects;
import java.lang.StringBuilder;

public class Main {
  public static void main(String[] args ){

    Scanner sc = new Scanner(System.in);

    int N = sc.nextInt();
    int K = sc.nextInt();

    StringBuilder S = new StringBuilder(sc.next());

    char lower = Character.toLowerCase(S.charAt(K - 1));
    S.setCharAt(K - 1, lower);
    System.out.println(S.toString());
  }
}

/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