import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = Integer.parseInt(sc.next());
        int k = Integer.parseInt(sc.next());
        String s = sc.next();
        char[] charArray = s.toCharArray();

        if (charArray[k - 1] == 'A') {
            charArray[k - 1] = 'a';
        } else if (charArray[k - 1] == 'B') {
            charArray[k - 1] = 'b';
        } else {
            charArray[k - 1] = 'c';
        }

        System.out.println(String.valueOf(charArray));
    }
}

/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