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();
        int b = (int) s.charAt(k-1);
        b+=32;
		System.out.println(s.substring(0,k-1)+(char)b+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