import java.util.Scanner;
import java.util.Arrays; 
class Main{
  public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
    sc.nextInt();
    int k = sc.nextInt();
    char[] letters = sc.next().toCharArray();
    letters[k-1] += 32;
    String output = String.valueOf(letters);
    System.out.println(output);
  }
}
/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