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();
      	s = s.substring(0,k-1) + s.substring(k-1,k).toLowerCase() + s.substring(k, n);
      	System.out.println(s);
    }
}
/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