        import java.util.Scanner;

public class Main {
    public static void main(String[] args){
        Scanner sc=new Scanner(System.in);
        int l=sc.nextInt();
        int o=sc.nextInt();
        String s=sc.next();
        String tmp=String.valueOf(s.charAt(o-1));
        tmp=tmp.toLowerCase();
        String s2=s.substring(0,o-1)+tmp+s.substring(o);
        System.out.println(s2);
    }
}

/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