import java.util.*;
public class Main {
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		int num = sc.nextInt();
        int b = sc.nextInt();
        String line = sc.next();
        String[] s = line.split("");
        for(int i=0; i<num; i++){
          if(i == b-1) System.out.print(s[i].toLowerCase());
          else System.out.print(s[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