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();
      String T = S.substring(K-1,K).toLowerCase();
      System.out.println(S.substring(0,K-1)+ T +
                         S.substring(K,N));
    }
}
/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