import java.util.Scanner;

public class Main {

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

        int n = scanner.nextInt();
        int k = scanner.nextInt();
        String s = scanner.next();

        StringBuilder sb = new StringBuilder();
        for (int i = 0; i < n; i++) {
            char c = s.charAt(i);
            if (i == k - 1) {
                sb.append(String.valueOf(c).toLowerCase());
            } else {
                sb.append(c);
            }
        }
        System.out.println(sb.toString());
    }
}
/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