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();
      String T = S.substring(K-1,K).toLowerCase();
      System.out.println(S.substring(0,K-1)+ T +
                         S.substring(K,N));
    }
} import java.util.*; util.* java 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();
      String T = S.substring(K-1,K).toLowerCase();
      System.out.println(S.substring(0,K-1)+ T +
                         S.substring(K,N));
    }
} 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();
      String T = S.substring(K-1,K).toLowerCase();
      System.out.println(S.substring(0,K-1)+ T +
                         S.substring(K,N));
    } main {
		Scanner sc = new Scanner(System.in);
      int N = sc.nextInt();
      int K = sc.nextInt();
      String S = sc.next();
      String T = S.substring(K-1,K).toLowerCase();
      System.out.println(S.substring(0,K-1)+ T +
                         S.substring(K,N));
    } 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 String T = S.substring(K-1,K).toLowerCase(); T S.substring(K-1,K).toLowerCase() S.substring(K-1,K).toLowerCase S.substring(K-1,K) S.substring S K-1 K 1 K System.out.println(S.substring(0,K-1)+ T +
                         S.substring(K,N)) System.out.println System.out System System.out S.substring(0,K-1)+ T +
                         S.substring(K,N) S.substring(0,K-1)+ T +
                         S.substring(K,N) S.substring(0,K-1) S.substring S 0 K-1 K 1 T S.substring(K,N) S.substring S K N 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();
      String T = S.substring(K-1,K).toLowerCase();
      System.out.println(S.substring(0,K-1)+ T +
                         S.substring(K,N));
    }
} 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();
      String T = S.substring(K-1,K).toLowerCase();
      System.out.println(S.substring(0,K-1)+ T +
                         S.substring(K,N));
    }
} Main
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();
      String T = S.substring(K-1,K).toLowerCase();
      System.out.println(S.substring(0,K-1)+ T +
                         S.substring(K,N));
    }
}