import java.util.*;
import java.math.*;
import java.io.*;


public class Main {
    static Scanner sc = new Scanner(System.in);
    public static void main(String args[]) {
        int n = sc.nextInt();
        int k = sc.nextInt();
        String s = sc.next();
        for(int i = 0; i < n; i++) {
            if(i == k -1) {
                System.out.print(Character.toLowerCase(s.charAt(i)));
            } else {
                System.out.print(s.charAt(i));
            }
        }
        System.out.println();
    }
} import java.util.*; util.* java import java.math.*; math.* java import java.io.*; io.* java public class Main {
    static Scanner sc = new Scanner(System.in);
    public static void main(String args[]) {
        int n = sc.nextInt();
        int k = sc.nextInt();
        String s = sc.next();
        for(int i = 0; i < n; i++) {
            if(i == k -1) {
                System.out.print(Character.toLowerCase(s.charAt(i)));
            } else {
                System.out.print(s.charAt(i));
            }
        }
        System.out.println();
    }
} Main static Scanner sc = new Scanner(System.in); sc new Scanner(System.in) public static void main(String args[]) {
        int n = sc.nextInt();
        int k = sc.nextInt();
        String s = sc.next();
        for(int i = 0; i < n; i++) {
            if(i == k -1) {
                System.out.print(Character.toLowerCase(s.charAt(i)));
            } else {
                System.out.print(s.charAt(i));
            }
        }
        System.out.println();
    } main {
        int n = sc.nextInt();
        int k = sc.nextInt();
        String s = sc.next();
        for(int i = 0; i < n; i++) {
            if(i == k -1) {
                System.out.print(Character.toLowerCase(s.charAt(i)));
            } else {
                System.out.print(s.charAt(i));
            }
        }
        System.out.println();
    } 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 for(int i = 0; i < n; i++) {
            if(i == k -1) {
                System.out.print(Character.toLowerCase(s.charAt(i)));
            } else {
                System.out.print(s.charAt(i));
            }
        } int i = 0; int i = 0; i 0 i < n i n i++ i++ i {
            if(i == k -1) {
                System.out.print(Character.toLowerCase(s.charAt(i)));
            } else {
                System.out.print(s.charAt(i));
            }
        } {
            if(i == k -1) {
                System.out.print(Character.toLowerCase(s.charAt(i)));
            } else {
                System.out.print(s.charAt(i));
            }
        } if(i == k -1) {
                System.out.print(Character.toLowerCase(s.charAt(i)));
            } else {
                System.out.print(s.charAt(i));
            } i == k -1 i k -1 k 1 {
                System.out.print(Character.toLowerCase(s.charAt(i)));
            } System.out.print(Character.toLowerCase(s.charAt(i))) System.out.print System.out System System.out Character.toLowerCase(s.charAt(i)) Character.toLowerCase Character s.charAt(i) s.charAt s i {
                System.out.print(s.charAt(i));
            } System.out.print(s.charAt(i)) System.out.print System.out System System.out s.charAt(i) s.charAt s i System.out.println() System.out.println System.out System System.out String args[] args public class Main {
    static Scanner sc = new Scanner(System.in);
    public static void main(String args[]) {
        int n = sc.nextInt();
        int k = sc.nextInt();
        String s = sc.next();
        for(int i = 0; i < n; i++) {
            if(i == k -1) {
                System.out.print(Character.toLowerCase(s.charAt(i)));
            } else {
                System.out.print(s.charAt(i));
            }
        }
        System.out.println();
    }
} public class Main {
    static Scanner sc = new Scanner(System.in);
    public static void main(String args[]) {
        int n = sc.nextInt();
        int k = sc.nextInt();
        String s = sc.next();
        for(int i = 0; i < n; i++) {
            if(i == k -1) {
                System.out.print(Character.toLowerCase(s.charAt(i)));
            } else {
                System.out.print(s.charAt(i));
            }
        }
        System.out.println();
    }
} Main
import java.util.*;
import java.math.*;
import java.io.*;


public class Main {
    static Scanner sc = new Scanner(System.in);
    public static void main(String args[]) {
        int n = sc.nextInt();
        int k = sc.nextInt();
        String s = sc.next();
        for(int i = 0; i < n; i++) {
            if(i == k -1) {
                System.out.print(Character.toLowerCase(s.charAt(i)));
            } else {
                System.out.print(s.charAt(i));
            }
        }
        System.out.println();
    }
}