import java.util.Scanner;

public class Main {

    public static void main(String[] args) {
        
        Scanner sc = new Scanner(System.in);
        
        sc.next();
        int k = Integer.parseInt(sc.next());
        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(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