import java.util.*;
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();
      
        int count = 0;
        char[] c = S.toCharArray();
        for(char c1 : c) {
            count++;
            if (count!= K){
            System.out.print(c1);
            }else{
            String tmp = String.valueOf(c1);
            System.out.print(tmp.toLowerCase());
            
            }
          
        }
        
        
    System.out.println();
    }
}
 import java.util.*; util.* java 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();
      
        int count = 0;
        char[] c = S.toCharArray();
        for(char c1 : c) {
            count++;
            if (count!= K){
            System.out.print(c1);
            }else{
            String tmp = String.valueOf(c1);
            System.out.print(tmp.toLowerCase());
            
            }
          
        }
        
        
    System.out.println();
    }
} 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();
      
        int count = 0;
        char[] c = S.toCharArray();
        for(char c1 : c) {
            count++;
            if (count!= K){
            System.out.print(c1);
            }else{
            String tmp = String.valueOf(c1);
            System.out.print(tmp.toLowerCase());
            
            }
          
        }
        
        
    System.out.println();
    } main {
        Scanner sc = new Scanner(System.in);
        int N = sc.nextInt();
        int K = sc.nextInt();
        String S = sc.next();
      
        int count = 0;
        char[] c = S.toCharArray();
        for(char c1 : c) {
            count++;
            if (count!= K){
            System.out.print(c1);
            }else{
            String tmp = String.valueOf(c1);
            System.out.print(tmp.toLowerCase());
            
            }
          
        }
        
        
    System.out.println();
    } 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 int count = 0; count 0 char[] c = S.toCharArray(); c S.toCharArray() S.toCharArray S for(char c1 : c) {
            count++;
            if (count!= K){
            System.out.print(c1);
            }else{
            String tmp = String.valueOf(c1);
            System.out.print(tmp.toLowerCase());
            
            }
          
        } char c1 c {
            count++;
            if (count!= K){
            System.out.print(c1);
            }else{
            String tmp = String.valueOf(c1);
            System.out.print(tmp.toLowerCase());
            
            }
          
        } {
            count++;
            if (count!= K){
            System.out.print(c1);
            }else{
            String tmp = String.valueOf(c1);
            System.out.print(tmp.toLowerCase());
            
            }
          
        } count++ count if (count!= K){
            System.out.print(c1);
            }else{
            String tmp = String.valueOf(c1);
            System.out.print(tmp.toLowerCase());
            
            } count!= K count K {
            System.out.print(c1);
            } System.out.print(c1) System.out.print System.out System System.out c1 {
            String tmp = String.valueOf(c1);
            System.out.print(tmp.toLowerCase());
            
            } String tmp = String.valueOf(c1); tmp String.valueOf(c1) String.valueOf String c1 System.out.print(tmp.toLowerCase()) System.out.print System.out System System.out tmp.toLowerCase() tmp.toLowerCase tmp System.out.println() System.out.println System.out System System.out String[] args args
import java.util.*;
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();
      
        int count = 0;
        char[] c = S.toCharArray();
        for(char c1 : c) {
            count++;
            if (count!= K){
            System.out.print(c1);
            }else{
            String tmp = String.valueOf(c1);
            System.out.print(tmp.toLowerCase());
            
            }
          
        }
        
        
    System.out.println();
    }
}

