import java.util.*;

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

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

    char[] c = s.toCharArray();
    char target = c[k - 1];
    char replaced = Character.toLowerCase(target);

    StringBuilder sb = new StringBuilder(s);
    sb.setCharAt(k - 1, replaced);

    System.out.println(sb);
    
  }
}
/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