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();
        char[]ss = S.toCharArray();

            if(ss[K-1]=='A'){
                ss[K-1]='a';
                System.out.println(String.valueOf(ss)); 
            }else if(ss[K-1]=='B'){
                 ss[K-1]='b';
                System.out.println(String.valueOf(ss)); 
            }else{
                 ss[K-1]='c';
                System.out.println(String.valueOf(ss));            
            }
 	    }
}

/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