import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		Scanner scanner = new Scanner(System.in);

		int n = scanner.nextInt();
		int k = scanner.nextInt();
		String s = scanner.next();

		char conv = Character.toLowerCase(s.charAt(k - 1));
		String pre = (k == 1 ? "" : s.substring(0, k - 1));
		String next = (k == n ? "" : s.substring(k));

		System.out.println(pre + conv + next);
	}
}
/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