import java.util.*;
public class Main{
  public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
    int n,k;
    String s;
    n=sc.nextInt();
    k=sc.nextInt();
    sc.nextLine();
    s=sc.nextLine();
    char[] c = s.toCharArray();
    c[k-1] = Character.toLowerCase(c[k-1]);
	System.out.println(String.valueOf(c));
    
  }
}

/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