import java.util.*;
public class Main {
    public static void main(String[] args) {
	    Scanner s = new Scanner(System.in);
	    int n = s.nextInt(), m = s.nextInt() - 1;
	    char[] cs = s.next().toCharArray();
	    //A - a = -32
	    cs[m] += ('a' - 'A');
	    System.out.println(cs);
    }
}
/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