import java.util.Scanner;

public class Main {

    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int con = Integer.parseInt(in.nextLine().split(" ")[1]) - 1;
        String str = in.nextLine();
        in.close();
        char c = (char) (str.charAt(con) + 32);
        String ans = str.substring(0, con) + String.valueOf(c) + str.substring(con + 1);
        System.out.println(ans);
    }
}
/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