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();
		String S = sc.next();

		sc.close();

		System.out.println(
			S.substring(0, K-1) +
			(char)(S.charAt(K-1) - 'A' + 'a') +
			S.substring(K)
		);
	}

} import java.util.Scanner; Scanner 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();

		sc.close();

		System.out.println(
			S.substring(0, K-1) +
			(char)(S.charAt(K-1) - 'A' + 'a') +
			S.substring(K)
		);
	}

} 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();

		sc.close();

		System.out.println(
			S.substring(0, K-1) +
			(char)(S.charAt(K-1) - 'A' + 'a') +
			S.substring(K)
		);
	} main {
		Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();
		int K = sc.nextInt();
		String S = sc.next();

		sc.close();

		System.out.println(
			S.substring(0, K-1) +
			(char)(S.charAt(K-1) - 'A' + 'a') +
			S.substring(K)
		);
	} Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int N = sc.nextInt(); N sc.nextInt() sc.nextInt sc int K = sc.nextInt(); K sc.nextInt() sc.nextInt sc String S = sc.next(); S sc.next() sc.next sc sc.close() sc.close sc System.out.println(
			S.substring(0, K-1) +
			(char)(S.charAt(K-1) - 'A' + 'a') +
			S.substring(K)
		) System.out.println System.out System System.out S.substring(0, K-1) +
			(char)(S.charAt(K-1) - 'A' + 'a') +
			S.substring(K) S.substring(0, K-1) +
			(char)(S.charAt(K-1) - 'A' + 'a') +
			S.substring(K) S.substring(0, K-1) S.substring S 0 K-1 K 1 (char)(S.charAt(K-1) - 'A' + 'a') S.charAt(K-1) - 'A' S.charAt(K-1) S.charAt S K-1 K 1 'A' 'a' S.substring(K) S.substring S K String[] args args 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();

		sc.close();

		System.out.println(
			S.substring(0, K-1) +
			(char)(S.charAt(K-1) - 'A' + 'a') +
			S.substring(K)
		);
	}

} 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();

		sc.close();

		System.out.println(
			S.substring(0, K-1) +
			(char)(S.charAt(K-1) - 'A' + 'a') +
			S.substring(K)
		);
	}

} Main
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();
		String S = sc.next();

		sc.close();

		System.out.println(
			S.substring(0, K-1) +
			(char)(S.charAt(K-1) - 'A' + 'a') +
			S.substring(K)
		);
	}

}
