import java.io.OutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.util.Scanner;

/**
 * Built using CHelper plug-in
 * Actual solution is at the top
 */
public class Main {
    public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        Scanner in = new Scanner(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        A solver = new A();
        solver.solve(1, in, out);
        out.close();
    }

    static class A {
        public void solve(int testNumber, Scanner in, PrintWriter out) {
            // 入力
            int n = Integer.parseInt(in.next());
            int k = Integer.parseInt(in.next());
            String S = in.next();
            String tmp1 = S.substring(0, k - 1);
            String tmp2 = S.substring(k);
            Character tmp3 = Character.toLowerCase(S.charAt(k - 1));

            // 出力
            out.println(tmp1 + tmp3 + tmp2);

        }

    }
}
 import java.io.OutputStream; OutputStream java.io import java.io.IOException; IOException java.io import java.io.InputStream; InputStream java.io import java.io.PrintWriter; PrintWriter java.io import java.util.Scanner; Scanner java.util public class Main {
    public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        Scanner in = new Scanner(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        A solver = new A();
        solver.solve(1, in, out);
        out.close();
    }

    static class A {
        public void solve(int testNumber, Scanner in, PrintWriter out) {
            // 入力
            int n = Integer.parseInt(in.next());
            int k = Integer.parseInt(in.next());
            String S = in.next();
            String tmp1 = S.substring(0, k - 1);
            String tmp2 = S.substring(k);
            Character tmp3 = Character.toLowerCase(S.charAt(k - 1));

            // 出力
            out.println(tmp1 + tmp3 + tmp2);

        }

    }
} Main public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        Scanner in = new Scanner(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        A solver = new A();
        solver.solve(1, in, out);
        out.close();
    } main {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        Scanner in = new Scanner(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        A solver = new A();
        solver.solve(1, in, out);
        out.close();
    } InputStream inputStream = System.in; inputStream System.in System System.in OutputStream outputStream = System.out; outputStream System.out System System.out Scanner in = new Scanner(inputStream); in new Scanner(inputStream) PrintWriter out = new PrintWriter(outputStream); out new PrintWriter(outputStream) A solver = new A(); solver new A() solver.solve(1, in, out) solver.solve solver 1 in out out.close() out.close out String[] args args static class A {
        public void solve(int testNumber, Scanner in, PrintWriter out) {
            // 入力
            int n = Integer.parseInt(in.next());
            int k = Integer.parseInt(in.next());
            String S = in.next();
            String tmp1 = S.substring(0, k - 1);
            String tmp2 = S.substring(k);
            Character tmp3 = Character.toLowerCase(S.charAt(k - 1));

            // 出力
            out.println(tmp1 + tmp3 + tmp2);

        }

    } A public void solve(int testNumber, Scanner in, PrintWriter out) {
            // 入力
            int n = Integer.parseInt(in.next());
            int k = Integer.parseInt(in.next());
            String S = in.next();
            String tmp1 = S.substring(0, k - 1);
            String tmp2 = S.substring(k);
            Character tmp3 = Character.toLowerCase(S.charAt(k - 1));

            // 出力
            out.println(tmp1 + tmp3 + tmp2);

        } solve {
            // 入力
            int n = Integer.parseInt(in.next());
            int k = Integer.parseInt(in.next());
            String S = in.next();
            String tmp1 = S.substring(0, k - 1);
            String tmp2 = S.substring(k);
            Character tmp3 = Character.toLowerCase(S.charAt(k - 1));

            // 出力
            out.println(tmp1 + tmp3 + tmp2);

        } int n = Integer.parseInt(in.next()); n Integer.parseInt(in.next()) Integer.parseInt Integer in.next() in.next in int k = Integer.parseInt(in.next()); k Integer.parseInt(in.next()) Integer.parseInt Integer in.next() in.next in String S = in.next(); S in.next() in.next in String tmp1 = S.substring(0, k - 1); tmp1 S.substring(0, k - 1) S.substring S 0 k - 1 k 1 String tmp2 = S.substring(k); tmp2 S.substring(k) S.substring S k Character tmp3 = Character.toLowerCase(S.charAt(k - 1)); tmp3 Character.toLowerCase(S.charAt(k - 1)) Character.toLowerCase Character S.charAt(k - 1) S.charAt S k - 1 k 1 out.println(tmp1 + tmp3 + tmp2) out.println out tmp1 + tmp3 + tmp2 tmp1 + tmp3 + tmp2 tmp1 tmp3 tmp2 int testNumber testNumber Scanner in in PrintWriter out out public class Main {
    public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        Scanner in = new Scanner(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        A solver = new A();
        solver.solve(1, in, out);
        out.close();
    }

    static class A {
        public void solve(int testNumber, Scanner in, PrintWriter out) {
            // 入力
            int n = Integer.parseInt(in.next());
            int k = Integer.parseInt(in.next());
            String S = in.next();
            String tmp1 = S.substring(0, k - 1);
            String tmp2 = S.substring(k);
            Character tmp3 = Character.toLowerCase(S.charAt(k - 1));

            // 出力
            out.println(tmp1 + tmp3 + tmp2);

        }

    }
} public class Main {
    public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        Scanner in = new Scanner(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        A solver = new A();
        solver.solve(1, in, out);
        out.close();
    }

    static class A {
        public void solve(int testNumber, Scanner in, PrintWriter out) {
            // 入力
            int n = Integer.parseInt(in.next());
            int k = Integer.parseInt(in.next());
            String S = in.next();
            String tmp1 = S.substring(0, k - 1);
            String tmp2 = S.substring(k);
            Character tmp3 = Character.toLowerCase(S.charAt(k - 1));

            // 出力
            out.println(tmp1 + tmp3 + tmp2);

        }

    }
} Main
import java.io.OutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.util.Scanner;

/**
 * Built using CHelper plug-in
 * Actual solution is at the top
 */
public class Main {
    public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        Scanner in = new Scanner(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        A solver = new A();
        solver.solve(1, in, out);
        out.close();
    }

    static class A {
        public void solve(int testNumber, Scanner in, PrintWriter out) {
            // 入力
            int n = Integer.parseInt(in.next());
            int k = Integer.parseInt(in.next());
            String S = in.next();
            String tmp1 = S.substring(0, k - 1);
            String tmp2 = S.substring(k);
            Character tmp3 = Character.toLowerCase(S.charAt(k - 1));

            // 出力
            out.println(tmp1 + tmp3 + tmp2);

        }

    }
}

