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

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();
		
		for(int i = 0; i < s.length(); i++) {
			if(i+1 == k) {
				System.out.print(Character.toLowerCase(s.charAt(i)));
			} else {
				System.out.print(s.charAt(i));
			}
		}
	}
} import java.util.*; util.* java import java.io.*; io.* 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();
		
		for(int i = 0; i < s.length(); i++) {
			if(i+1 == k) {
				System.out.print(Character.toLowerCase(s.charAt(i)));
			} else {
				System.out.print(s.charAt(i));
			}
		}
	}
} 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();
		
		for(int i = 0; i < s.length(); i++) {
			if(i+1 == k) {
				System.out.print(Character.toLowerCase(s.charAt(i)));
			} else {
				System.out.print(s.charAt(i));
			}
		}
	} main {
		Scanner sc = new Scanner(System.in);
		
		int n = sc.nextInt();
		int k = sc.nextInt();
		String s = sc.next();
		
		for(int i = 0; i < s.length(); i++) {
			if(i+1 == k) {
				System.out.print(Character.toLowerCase(s.charAt(i)));
			} else {
				System.out.print(s.charAt(i));
			}
		}
	} 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 for(int i = 0; i < s.length(); i++) {
			if(i+1 == k) {
				System.out.print(Character.toLowerCase(s.charAt(i)));
			} else {
				System.out.print(s.charAt(i));
			}
		} int i = 0; int i = 0; i 0 i < s.length() i s.length() s.length s i++ i++ i {
			if(i+1 == k) {
				System.out.print(Character.toLowerCase(s.charAt(i)));
			} else {
				System.out.print(s.charAt(i));
			}
		} {
			if(i+1 == k) {
				System.out.print(Character.toLowerCase(s.charAt(i)));
			} else {
				System.out.print(s.charAt(i));
			}
		} if(i+1 == k) {
				System.out.print(Character.toLowerCase(s.charAt(i)));
			} else {
				System.out.print(s.charAt(i));
			} i+1 == k i+1 i 1 k {
				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 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();
		
		for(int i = 0; i < s.length(); i++) {
			if(i+1 == k) {
				System.out.print(Character.toLowerCase(s.charAt(i)));
			} else {
				System.out.print(s.charAt(i));
			}
		}
	}
} 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();
		
		for(int i = 0; i < s.length(); i++) {
			if(i+1 == k) {
				System.out.print(Character.toLowerCase(s.charAt(i)));
			} else {
				System.out.print(s.charAt(i));
			}
		}
	}
} Main
import java.util.*;
import java.io.*;

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();
		
		for(int i = 0; i < s.length(); i++) {
			if(i+1 == k) {
				System.out.print(Character.toLowerCase(s.charAt(i)));
			} else {
				System.out.print(s.charAt(i));
			}
		}
	}
}
