    import java.util.*;
     public class Main{
     public static void main(String args[]){
                
       Scanner sc = new Scanner(System.in);
            
       int a = sc.nextInt();
       int b = sc.nextInt();
       String x = sc.nextLine();
       String c = sc.nextLine();
                
       if(b == 1){
         System.out.println(c.substring(0,1).toLowerCase() + c.substring(1));
       }else if(b < a){
         System.out.println(c.substring(0,b-1) + c.substring(b-1,b).toLowerCase() + c.substring(b));
       }else{
         System.out.println(c.substring(0,b-1) + c.substring(b-1).toLowerCase());
       }
     }
    }
/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