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

public class Main {
  public static void main(String[] args) throws IOException {
    BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
    String[] strs =  br.readLine().split(" ");
    int N = Integer.parseInt(strs[0]);
    int K = Integer.parseInt(strs[1]) - 1;
    String s = br.readLine();
    String[] tmp = new String[N];
    for (int i = 0; i < N; i++) {
      tmp[i] = String.valueOf(s.charAt(i));
    }
    tmp[K] = tmp[K].toLowerCase();
    System.out.println(String.join("", tmp));
  }
}
/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