import java.util.*;
import java.math.*;
import java.lang.*;
import java.io.*;
 
public class Main{
  public static void main(String args[]) throws IOException{
    Scanner s=new Scanner(System.in);
   
    int n=s.nextInt();
   int k=s.nextInt();
    
    String ss=s.next();
    
    System.out.println(ss.substring(0,k-1)+(char)(ss.charAt(k-1)+32)+ss.substring(k));
  }
}
/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