import java.util.Arrays;
import java.util.List;
import java.util.Scanner;

public class Main {

	public static void main(String[] args) throws Exception {
		Main main = new Main();

		try (Scanner scan = new Scanner(System.in)) {
			main.changingACharchter(scan);
		}
	}

	private void changingACharchter(Scanner scan) {
		scan.nextInt();
		int k = scan.nextInt();
		char[] s = scan.next().toCharArray();

		s[k - 1] = Character.toLowerCase(s[k - 1]);
		System.out.println(new String(s));

	}

}

/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