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

public class Main {
    public static void main(String[] args) {
        FastReader fr = new FastReader();
        int N = fr.nextInt(), K = fr.nextInt();
        String S = fr.next();
        S = S.substring(0, K-1) + (char) (S.charAt(K-1) - 'A' + 'a') + S.substring(K);
        System.out.println(S);
    }
}

class FastReader {

    BufferedReader br;
    StringTokenizer st;

    public FastReader() {
        br = new BufferedReader(new InputStreamReader(System.in));
    }

    String next() {
        while (st == null || !st.hasMoreElements()) {
            try {
                st = new StringTokenizer(br.readLine());
            } catch (IOException  e) {
                e.printStackTrace();
            }
        }
        return st.nextToken();
    }

    int nextInt() {
        return Integer.parseInt(next());
    }

    long nextLong() {
        return Long.parseLong(next());
    }

    double nextDouble() {
        return Double.parseDouble(next());
    }

    String nextLine() {
        String str = "";
        try {
            str = br.readLine();
        } catch (IOException e) {
            e.printStackTrace();
        }
        return str;
    }
} import java.io.*; io.* java import java.util.*; util.* java public class Main {
    public static void main(String[] args) {
        FastReader fr = new FastReader();
        int N = fr.nextInt(), K = fr.nextInt();
        String S = fr.next();
        S = S.substring(0, K-1) + (char) (S.charAt(K-1) - 'A' + 'a') + S.substring(K);
        System.out.println(S);
    }
} Main public static void main(String[] args) {
        FastReader fr = new FastReader();
        int N = fr.nextInt(), K = fr.nextInt();
        String S = fr.next();
        S = S.substring(0, K-1) + (char) (S.charAt(K-1) - 'A' + 'a') + S.substring(K);
        System.out.println(S);
    } main {
        FastReader fr = new FastReader();
        int N = fr.nextInt(), K = fr.nextInt();
        String S = fr.next();
        S = S.substring(0, K-1) + (char) (S.charAt(K-1) - 'A' + 'a') + S.substring(K);
        System.out.println(S);
    } FastReader fr = new FastReader(); fr new FastReader() int N = fr.nextInt() N fr.nextInt() fr.nextInt fr K = fr.nextInt(); K fr.nextInt() fr.nextInt fr String S = fr.next(); S fr.next() fr.next fr S = S.substring(0, K-1) + (char) (S.charAt(K-1) - 'A' + 'a') + S.substring(K) S S.substring(0, K-1) + (char) (S.charAt(K-1) - 'A' + 'a') + S.substring(K) S.substring(0, K-1) + (char) (S.charAt(K-1) - 'A' + 'a') + S.substring(K) S.substring(0, K-1) S.substring S 0 K-1 K 1 (char) (S.charAt(K-1) - 'A' + 'a') S.charAt(K-1) - 'A' S.charAt(K-1) S.charAt S K-1 K 1 'A' 'a' S.substring(K) S.substring S K System.out.println(S) System.out.println System.out System System.out S String[] args args class FastReader {

    BufferedReader br;
    StringTokenizer st;

    public FastReader() {
        br = new BufferedReader(new InputStreamReader(System.in));
    }

    String next() {
        while (st == null || !st.hasMoreElements()) {
            try {
                st = new StringTokenizer(br.readLine());
            } catch (IOException  e) {
                e.printStackTrace();
            }
        }
        return st.nextToken();
    }

    int nextInt() {
        return Integer.parseInt(next());
    }

    long nextLong() {
        return Long.parseLong(next());
    }

    double nextDouble() {
        return Double.parseDouble(next());
    }

    String nextLine() {
        String str = "";
        try {
            str = br.readLine();
        } catch (IOException e) {
            e.printStackTrace();
        }
        return str;
    }
} FastReader BufferedReader br; br StringTokenizer st; st public FastReader() {
        br = new BufferedReader(new InputStreamReader(System.in));
    } FastReader {
        br = new BufferedReader(new InputStreamReader(System.in));
    } br = new BufferedReader(new InputStreamReader(System.in)) br new BufferedReader(new InputStreamReader(System.in)) String next() {
        while (st == null || !st.hasMoreElements()) {
            try {
                st = new StringTokenizer(br.readLine());
            } catch (IOException  e) {
                e.printStackTrace();
            }
        }
        return st.nextToken();
    } next {
        while (st == null || !st.hasMoreElements()) {
            try {
                st = new StringTokenizer(br.readLine());
            } catch (IOException  e) {
                e.printStackTrace();
            }
        }
        return st.nextToken();
    } while (st == null || !st.hasMoreElements()) {
            try {
                st = new StringTokenizer(br.readLine());
            } catch (IOException  e) {
                e.printStackTrace();
            }
        } st == null || !st.hasMoreElements() st == null st null !st.hasMoreElements() st.hasMoreElements() st.hasMoreElements st {
            try {
                st = new StringTokenizer(br.readLine());
            } catch (IOException  e) {
                e.printStackTrace();
            }
        } try {
                st = new StringTokenizer(br.readLine());
            } catch (IOException  e) {
                e.printStackTrace();
            } catch (IOException  e) {
                e.printStackTrace();
            } IOException  e {
                e.printStackTrace();
            } e.printStackTrace() e.printStackTrace e {
                st = new StringTokenizer(br.readLine());
            } st = new StringTokenizer(br.readLine()) st new StringTokenizer(br.readLine()) return st.nextToken(); st.nextToken() st.nextToken st int nextInt() {
        return Integer.parseInt(next());
    } nextInt {
        return Integer.parseInt(next());
    } return Integer.parseInt(next()); Integer.parseInt(next()) Integer.parseInt Integer next() next long nextLong() {
        return Long.parseLong(next());
    } nextLong {
        return Long.parseLong(next());
    } return Long.parseLong(next()); Long.parseLong(next()) Long.parseLong Long next() next double nextDouble() {
        return Double.parseDouble(next());
    } nextDouble {
        return Double.parseDouble(next());
    } return Double.parseDouble(next()); Double.parseDouble(next()) Double.parseDouble Double next() next String nextLine() {
        String str = "";
        try {
            str = br.readLine();
        } catch (IOException e) {
            e.printStackTrace();
        }
        return str;
    } nextLine {
        String str = "";
        try {
            str = br.readLine();
        } catch (IOException e) {
            e.printStackTrace();
        }
        return str;
    } String str = ""; str "" try {
            str = br.readLine();
        } catch (IOException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } IOException e {
            e.printStackTrace();
        } e.printStackTrace() e.printStackTrace e {
            str = br.readLine();
        } str = br.readLine() str br.readLine() br.readLine br return str; str public class Main {
    public static void main(String[] args) {
        FastReader fr = new FastReader();
        int N = fr.nextInt(), K = fr.nextInt();
        String S = fr.next();
        S = S.substring(0, K-1) + (char) (S.charAt(K-1) - 'A' + 'a') + S.substring(K);
        System.out.println(S);
    }
} public class Main {
    public static void main(String[] args) {
        FastReader fr = new FastReader();
        int N = fr.nextInt(), K = fr.nextInt();
        String S = fr.next();
        S = S.substring(0, K-1) + (char) (S.charAt(K-1) - 'A' + 'a') + S.substring(K);
        System.out.println(S);
    }
} Main
import java.io.*;
import java.util.*;

public class Main {
    public static void main(String[] args) {
        FastReader fr = new FastReader();
        int N = fr.nextInt(), K = fr.nextInt();
        String S = fr.next();
        S = S.substring(0, K-1) + (char) (S.charAt(K-1) - 'A' + 'a') + S.substring(K);
        System.out.println(S);
    }
}

class FastReader {

    BufferedReader br;
    StringTokenizer st;

    public FastReader() {
        br = new BufferedReader(new InputStreamReader(System.in));
    }

    String next() {
        while (st == null || !st.hasMoreElements()) {
            try {
                st = new StringTokenizer(br.readLine());
            } catch (IOException  e) {
                e.printStackTrace();
            }
        }
        return st.nextToken();
    }

    int nextInt() {
        return Integer.parseInt(next());
    }

    long nextLong() {
        return Long.parseLong(next());
    }

    double nextDouble() {
        return Double.parseDouble(next());
    }

    String nextLine() {
        String str = "";
        try {
            str = br.readLine();
        } catch (IOException e) {
            e.printStackTrace();
        }
        return str;
    }
}