import java.util.HashMap;
import java.util.Map;
import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner std = new Scanner(System.in);
        int n = std.nextInt();
        int k = std.nextInt();
        String s = std.next();
        StringBuilder sb = new StringBuilder();
        Map<Character, Character> mapping = new HashMap<>();
        mapping.put('A', 'a');
        mapping.put('B', 'b');
        mapping.put('C', 'c');

        for (int i = 0; i < n; i++) {
            Character c = s.charAt(i);
            if (i == k - 1) {
                sb.append(mapping.get(c));
            } else {
                sb.append(c);
            }
        }

        System.out.println(sb.toString());
    }
} import java.util.HashMap; HashMap java.util import java.util.Map; Map java.util import java.util.Scanner; Scanner java.util public class Main {
    public static void main(String[] args) {
        Scanner std = new Scanner(System.in);
        int n = std.nextInt();
        int k = std.nextInt();
        String s = std.next();
        StringBuilder sb = new StringBuilder();
        Map<Character, Character> mapping = new HashMap<>();
        mapping.put('A', 'a');
        mapping.put('B', 'b');
        mapping.put('C', 'c');

        for (int i = 0; i < n; i++) {
            Character c = s.charAt(i);
            if (i == k - 1) {
                sb.append(mapping.get(c));
            } else {
                sb.append(c);
            }
        }

        System.out.println(sb.toString());
    }
} Main public static void main(String[] args) {
        Scanner std = new Scanner(System.in);
        int n = std.nextInt();
        int k = std.nextInt();
        String s = std.next();
        StringBuilder sb = new StringBuilder();
        Map<Character, Character> mapping = new HashMap<>();
        mapping.put('A', 'a');
        mapping.put('B', 'b');
        mapping.put('C', 'c');

        for (int i = 0; i < n; i++) {
            Character c = s.charAt(i);
            if (i == k - 1) {
                sb.append(mapping.get(c));
            } else {
                sb.append(c);
            }
        }

        System.out.println(sb.toString());
    } main {
        Scanner std = new Scanner(System.in);
        int n = std.nextInt();
        int k = std.nextInt();
        String s = std.next();
        StringBuilder sb = new StringBuilder();
        Map<Character, Character> mapping = new HashMap<>();
        mapping.put('A', 'a');
        mapping.put('B', 'b');
        mapping.put('C', 'c');

        for (int i = 0; i < n; i++) {
            Character c = s.charAt(i);
            if (i == k - 1) {
                sb.append(mapping.get(c));
            } else {
                sb.append(c);
            }
        }

        System.out.println(sb.toString());
    } Scanner std = new Scanner(System.in); std new Scanner(System.in) int n = std.nextInt(); n std.nextInt() std.nextInt std int k = std.nextInt(); k std.nextInt() std.nextInt std String s = std.next(); s std.next() std.next std StringBuilder sb = new StringBuilder(); sb new StringBuilder() Map<Character, Character> mapping = new HashMap<>(); mapping new HashMap<>() mapping.put('A', 'a') mapping.put mapping 'A' 'a' mapping.put('B', 'b') mapping.put mapping 'B' 'b' mapping.put('C', 'c') mapping.put mapping 'C' 'c' for (int i = 0; i < n; i++) {
            Character c = s.charAt(i);
            if (i == k - 1) {
                sb.append(mapping.get(c));
            } else {
                sb.append(c);
            }
        } int i = 0; int i = 0; i 0 i < n i n i++ i++ i {
            Character c = s.charAt(i);
            if (i == k - 1) {
                sb.append(mapping.get(c));
            } else {
                sb.append(c);
            }
        } {
            Character c = s.charAt(i);
            if (i == k - 1) {
                sb.append(mapping.get(c));
            } else {
                sb.append(c);
            }
        } Character c = s.charAt(i); c s.charAt(i) s.charAt s i if (i == k - 1) {
                sb.append(mapping.get(c));
            } else {
                sb.append(c);
            } i == k - 1 i k - 1 k 1 {
                sb.append(mapping.get(c));
            } sb.append(mapping.get(c)) sb.append sb mapping.get(c) mapping.get mapping c {
                sb.append(c);
            } sb.append(c) sb.append sb c System.out.println(sb.toString()) System.out.println System.out System System.out sb.toString() sb.toString sb String[] args args public class Main {
    public static void main(String[] args) {
        Scanner std = new Scanner(System.in);
        int n = std.nextInt();
        int k = std.nextInt();
        String s = std.next();
        StringBuilder sb = new StringBuilder();
        Map<Character, Character> mapping = new HashMap<>();
        mapping.put('A', 'a');
        mapping.put('B', 'b');
        mapping.put('C', 'c');

        for (int i = 0; i < n; i++) {
            Character c = s.charAt(i);
            if (i == k - 1) {
                sb.append(mapping.get(c));
            } else {
                sb.append(c);
            }
        }

        System.out.println(sb.toString());
    }
} public class Main {
    public static void main(String[] args) {
        Scanner std = new Scanner(System.in);
        int n = std.nextInt();
        int k = std.nextInt();
        String s = std.next();
        StringBuilder sb = new StringBuilder();
        Map<Character, Character> mapping = new HashMap<>();
        mapping.put('A', 'a');
        mapping.put('B', 'b');
        mapping.put('C', 'c');

        for (int i = 0; i < n; i++) {
            Character c = s.charAt(i);
            if (i == k - 1) {
                sb.append(mapping.get(c));
            } else {
                sb.append(c);
            }
        }

        System.out.println(sb.toString());
    }
} Main
import java.util.HashMap;
import java.util.Map;
import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner std = new Scanner(System.in);
        int n = std.nextInt();
        int k = std.nextInt();
        String s = std.next();
        StringBuilder sb = new StringBuilder();
        Map<Character, Character> mapping = new HashMap<>();
        mapping.put('A', 'a');
        mapping.put('B', 'b');
        mapping.put('C', 'c');

        for (int i = 0; i < n; i++) {
            Character c = s.charAt(i);
            if (i == k - 1) {
                sb.append(mapping.get(c));
            } else {
                sb.append(c);
            }
        }

        System.out.println(sb.toString());
    }
}
