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();
		
        for(int i=0;i<N;i++){
          if (i+1 == K){
            System.out.print(Character.toLowerCase(S.charAt(i)));
          }else{
            System.out.print(S.charAt(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