import java.util.Scanner;
import java.util.Arrays;
import java.util.ArrayList;

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

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();
        S = S.substring(0,K-1)+S.substring(K-1,K).toLowerCase()+S.substring(K);
        System.out.println(S);
        }
}

