import java.util.Scanner;

public class Main {

    public static String process(int N, int K, String S) {
        return S.substring(0, K - 1) + S.substring(K - 1, K).toLowerCase() + S.substring(K);
    }

    // Util func

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);

        int N = sc.nextInt();
        int K = sc.nextInt();
        String S = sc.next();

        final String result = process(N, K, S);

        output(result);
    }

    private static void output(String result) {
        System.out.println(result);
    }
}

/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