import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		String num = sc.nextLine();
      	String[] numSpl = num.split(" ");
      	int n = Integer.parseInt(numSpl[0]);
      	int k = Integer.parseInt(numSpl[1]);
		String s = sc.nextLine();
		

		String[] spl = s.split("");
		StringBuilder sb = new StringBuilder();
		for(int i = 0; i < n;i++){
			if(i == k-1){
				sb.append(spl[i].toLowerCase());
			}else{
				sb.append(spl[i]);
			}
		}
		System.out.println(sb);
		sc.close();
	}
}
/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