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[]c = S.toCharArray();

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