import java.util.Scanner;

public class Main {

    public static void main(String args[]) {

        // 入力
        Scanner sc = new Scanner(System.in);
        Integer n = Integer.parseInt(sc.next());
        Integer k = Integer.parseInt(sc.next());
        String s = sc.next();

        // 主処理
        String result = "";
        for (int i = 0; i < n; i++) {
            result += (i == k - 1) ? String.valueOf(s.charAt(i)).toLowerCase() : s.charAt(i);
        }

        // 出力
        System.out.println(result);
        sc.close();
    }
}
/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