Language: C++

import java.io.BufferedReader;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.PrintWriter;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;
import java.util.HashMap;
import java.util.LinkedList;
import java.util.List;
import java.util.Map;
import java.util.StringTokenizer;
import java.util.TreeMap;
import java.util.TreeSet;


public class Main {

	static class Task {
		
		int NN = 200005;
		int MOD = 1000000007;
		int INF = 2000000000;
		long INFINITY = 2000000000000000000L;
		
		public void solve(InputReader in, PrintWriter out) {
			int n = in.nextInt(), k = in.nextInt() - 1;
			String s = in.next();
			StringBuilder ss = new StringBuilder();
			for(int i=0;i<n;++i) {
				if(i == k) {
					ss.append((char)(s.charAt(i)-'A'+'a'));
				} else {
					ss.append(s.charAt(i));
				}
			}
			out.println(ss.toString());
		}
		
	}
	
	static void prepareIO(boolean isFileIO) {
		//long t1 = System.currentTimeMillis();
		Task solver = new Task();
		// Standard IO
		if(!isFileIO) { 
			InputStream inputStream = System.in;
	        OutputStream outputStream = System.out;
	        InputReader in = new InputReader(inputStream);
	        PrintWriter out = new PrintWriter(outputStream);
	        solver.solve(in, out);
	        //out.println("time(s): " + (1.0*(System.currentTimeMillis()-t1))/1000.0);
	        out.close();
		}
        // File IO
		else {
			String IPfilePath = System.getProperty("user.home") + "/Downloads/ip.in";
	        String OPfilePath = System.getProperty("user.home") + "/Downloads/op.out";
	        InputReader fin = new InputReader(IPfilePath);
	        PrintWriter fout = null;
	        try {
				fout = new PrintWriter(new File(OPfilePath));
			} catch (FileNotFoundException e) {
				e.printStackTrace();
			}
	        solver.solve(fin, fout);
	        //fout.println("time(s): " + (1.0*(System.currentTimeMillis()-t1))/1000.0);
	        fout.close();
		}
	}
	
	public static void main(String[] args) {
        prepareIO(false);
	}
	
	static class InputReader {
        public BufferedReader reader;
        public StringTokenizer tokenizer;

        public InputReader(InputStream stream) {
            reader = new BufferedReader(new InputStreamReader(stream), 32768);
            tokenizer = null;
        }
        
        public InputReader(String filePath) {
        	File file = new File(filePath);
            try {
				reader = new BufferedReader(new FileReader(file));
			} catch (FileNotFoundException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			}
            tokenizer = null;
        }
        
        public String nextLine() {
        	String str = "";
        	try {
				str = reader.readLine();
			} catch (IOException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			}
        	return str;
        }
        
        public String next() {
            while (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    tokenizer = new StringTokenizer(reader.readLine());
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }
            return tokenizer.nextToken();
        }

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

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

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

}

Compiler output:
a.cc:1:1: error: 'import' does not name a type
    1 | import java.io.BufferedReader;
      | ^~~~~~
a.cc:1:1: note: C++20 'import' only available with '-fmodules-ts'
a.cc:2:1: error: 'import' does not name a type
    2 | import java.io.File;
      | ^~~~~~
a.cc:2:1: note: C++20 'import' only available with '-fmodules-ts'
a.cc:3:1: error: 'import' does not name a type
    3 | import java.io.FileNotFoundException;
      | ^~~~~~
a.cc:3:1: note: C++20 'import' only available with '-fmodules-ts'
a.cc:4:1: error: 'import' does not name a type
    4 | import java.io.FileReader;
      | ^~~~~~
a.cc:4:1: note: C++20 'import' only available with '-fmodules-ts'
a.cc:5:1: error: 'import' does not name a type
    5 | import java.io.IOException;
      | ^~~~~~
a.cc:5:1: note: C++20 'import' only available with '-fmodules-ts'
a.cc:6:1: error: 'import' does not name a type
    6 | import java.io.InputStream;
      | ^~~~~~
a.cc:6:1: note: C++20 'import' only available with '-fmodules-ts'
a.cc:7:1: error: 'import' does not name a type
    7 | import java.io.InputStreamReader;
      | ^~~~~~
a.cc:7:1: note: C++20 'import' only available with '-fmodules-ts'
a.cc:8:1: error: 'import' does not name a type
    8 | import java.io.OutputStream;
      | ^~~~~~
a.cc:8:1: note: C++20 'import' only available with '-fmodules-ts'
a.cc:9:1: error: 'import' does not name a type
    9 | import java.io.PrintWriter;
      | ^~~~~~
a.cc:9:1: note: C++20 'import' only available with '-fmodules-ts'
a.cc:10:1: error: 'import' does not name a type
   10 | import java.util.ArrayList;
      | ^~~~~~
a.cc:10:1: note: C++20 'import' only available with '-fmodules-ts'
a.cc:11:1: error: 'import' does not name a type
   11 | import java.util.Arrays;
      | ^~~~~~
a.cc:11:1: note: C++20 'import' only available with '-fmodules-ts'
a.cc:12:1: error: 'import' does not name a type
   12 | import java.util.Collection;
      | ^~~~~~
a.cc:12:1: note: C++20 'import' only available with '-fmodules-ts'
a.cc:13:1: error: 'import' does not name a type
   13 | import java.util.Collections;
      | ^~~~~~
a.cc:13:1: note: C++20 'import' only available with '-fmodules-ts'
a.cc:14:1: error: 'import' does not name a type
   14 | import java.util.HashMap;
      | ^~~~~~
a.cc:14:1: note: C++20 'import' only available with '-fmodules-ts'
a.cc:15:1: error: 'import' does not name a type
   15 | import java.util.LinkedList;
      | ^~~~~~
a.cc:15:1: note: C++20 'import' only available with '-fmodules-ts'
a.cc:16:1: error: 'import' does not name a type
   16 | import java.util.List;
      | ^~~~~~
a.cc:16:1: note: C++20 'import' only available with '-fmodules-ts'
a.cc:17:1: error: 'import' does not name a type
   17 | import java.util.Map;
      | ^~~~~~
a.cc:17:1: note: C++20 'import' only available with '-fmodules-ts'
a.cc:18:1: error: 'import' does not name a type
   18 | import java.util.StringTokenizer;
      | ^~~~~~
a.cc:18:1: note: C++20 'import' only available with '-fmodules-ts'
a.cc:19:1: error: 'import' does not name a type
   19 | import java.util.TreeMap;
      | ^~~~~~
a.cc:19:1: note: C++20 'import' only available with '-fmodules-ts'
a.cc:20:1: error: 'import' does not name a type
   20 | import java.util.TreeSet;
      | ^~~~~~
a.cc:20:1: note: C++20 'import' only available with '-fmodules-ts'
a.cc:23:1: error: expected unqualified-id before 'public'
   23 | public class Main {
      | ^~~~~~