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();
      	int i ;
     
  		String[] str = s.split("");
		String temp = str[k-1];
      
      	String  answer[] = new String[n] ;
	
      	for(i = 0; i <= n-1 ; i++){
        	if(i == k-1){
              	answer[i] = temp.toLowerCase();
            }else{
              	answer[i] = str[i];
        	}
        }
      	String r = String.join("", answer);
      	System.out.println(r);
	}
}
/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