
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.util.Scanner;

class Main {

	public static void main(String[] args) throws Exception {
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		Scanner scanner = new Scanner(br.readLine());
		scanner.nextInt();
		int k = scanner.nextInt() -1;
		scanner.close();
		String string = br.readLine();

		char characters[] = new char[string.length()];
		for(int i=0; i<string.length(); i++) {
			characters[i] = string.charAt(i);
		}
		characters[k] = Character.toLowerCase(characters[k]);
		System.out.println(String.valueOf(characters));

	}

}

/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