import java.util.*;

public class Main {
    public static void main(String[] args) {
        Scanner s = new Scanner(System.in);
        String[] in = s.nextLine().split(" ");
        int where = Integer.parseInt(in[1])-1;
        String t = s.nextLine();
        String r = "";
        int i=0;
        for(char c:t.toCharArray()){
            if(i == where){
                r += String.valueOf(c).toLowerCase();
            }else {
                r += c;
            }
            i++;
        }
        System.out.println(r);
    }
}
/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