import java.util.Scanner;
public class Main {
	public static void main(String args[]) {
		Scanner stdIn = new Scanner(System.in);
		int N = stdIn.nextInt();
		int K = stdIn.nextInt();
		String S = stdIn.next();
		
		String[] s = S.split("",0);
		
		s[K-1] = s[K-1].toLowerCase();
		
		String a = String.join("", s);
		
		System.out.println(a);
	}
}
/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