import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);

		int n = sc.nextInt();
		int m = sc.nextInt();
		String s = sc.next();

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

		int n = sc.nextInt();
		int m = sc.nextInt();
		String s = sc.next();

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

		int n = sc.nextInt();
		int m = sc.nextInt();
		String s = sc.next();

		for(int i = 0; i < n; i++) {
			if(i == m-1) {
				System.out.print(s.toLowerCase().charAt(i));
			} else {
				System.out.print(s.charAt(i));
			}
		}
		System.out.println();
	} main {
		Scanner sc = new Scanner(System.in);

		int n = sc.nextInt();
		int m = sc.nextInt();
		String s = sc.next();

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

		int n = sc.nextInt();
		int m = sc.nextInt();
		String s = sc.next();

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

		int n = sc.nextInt();
		int m = sc.nextInt();
		String s = sc.next();

		for(int i = 0; i < n; i++) {
			if(i == m-1) {
				System.out.print(s.toLowerCase().charAt(i));
			} else {
				System.out.print(s.charAt(i));
			}
		}
		System.out.println();
	}
} Main
import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);

		int n = sc.nextInt();
		int m = sc.nextInt();
		String s = sc.next();

		for(int i = 0; i < n; i++) {
			if(i == m-1) {
				System.out.print(s.toLowerCase().charAt(i));
			} else {
				System.out.print(s.charAt(i));
			}
		}
		System.out.println();
	}
}