import java.util.Scanner;

public class Main {
	public static void main(String[]args) {
		Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();
		int K = sc.nextInt() - 1;
		String S = sc.next();
		sc.close();
		String[] s = S.split("");
		s [K] = s[K].toLowerCase();
		StringBuffer bf = new StringBuffer();
		for(int i=0;i<N;i++) {
			bf.append(s[i]);
		}
	System.out.print(bf.toString());
	}
}
/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