import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class Main {

  public static void main(String[] args) {

    new Main().run();
  }
  public void run() {

    try(BufferedReader in = new BufferedReader(new InputStreamReader(System.in))) {
      String[] lines = in.readLine().split(" ");
      // int n = Integer.parseInt(lines[0]);
      int k = Integer.parseInt(lines[1]);
      String s = in.readLine();

      char[] as =s.toCharArray();
      as[k-1] = Character.toLowerCase(as[k-1]);

      String ans = new String(as);
      System.out.println(ans);
    }
    catch(IOException e) {

      System.err.println(e);
    }
  }
}
/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