import java.util.*;
class Main{
  public static void main(String args[]){
    Scanner sc = new Scanner(System.in);
    int a=sc.nextInt(),b=sc.nextInt();
    String  str = sc.next();
    String[] strarr = str.split("");
    if(strarr[b-1].equals("A")){
      strarr[b-1] = "a";
    }
    else if(strarr[b-1].equals("B")){
      strarr[b-1] = "b";
    }
    else if(strarr[b-1].equals("C")){
      strarr[b-1] = "c";
    }
    String str2 = String.join("",strarr);
    System.out.println(str2);
  }
}
/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