import java.util.*;
import java.io.*;

public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		
		int n = sc.nextInt();
		int k = sc.nextInt();
		String s = sc.next();
		
		for(int i = 0; i < s.length(); i++) {
			if(i+1 == k) {
				System.out.print(Character.toLowerCase(s.charAt(i)));
			} else {
				System.out.print(s.charAt(i));
			}
		}
	}
}

/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