import java.util.*;
public class Main{
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int N,K;
        String S;
        N = sc.nextInt();
        K = sc.nextInt();
        S = sc.next();
        String[] array = S.split("",0);
        for (int i = 0; i < N; i++) {
            if (i==K-1) array[i] = array[i].toLowerCase();            
            System.out.print(array[i]);
        }
    }
}
/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