Language: C++

import com.sun.deploy.ui.MacJavaTrayIcon;
import com.sun.tools.hat.internal.model.ReachableExcludes;
import jdk.nashorn.internal.runtime.WithObject;

import javax.swing.text.AsyncBoxView;
import java.io.*;
import java.math.BigInteger;
import java.util.*;

class Main {

    private static PrintWriter out;

    private static <T> void mprintln(T... ar) {
        for (T i : ar) {
            out.print(i + " ");
        }
        out.println();
    }

    public static void main(String[] args) throws FileNotFoundException {

        // Input from file
        // File inputFile = new File("JavaFile.txt");
        // File outputFile = new File("JavaOutputFile.txt");
        // FileReader fileReader = new FileReader(inputFile);
        // Here it ends

        MyScanner sc = new MyScanner();
        // MyScanner sc = new MyScanner(fileReader);

        out = new PrintWriter(new BufferedOutputStream(System.out)); // Output to console
        // out = new PrintWriter(new PrintStream(outputFile)); // Output to file

        getAns(sc);

        out.close();
    }

    /*
     *Don't use builtin function (Math.ceil)
     */

    static final long MOD = (long) (1e9 + 7);

    private static void getAns(MyScanner sc) {
        long r = sc.nl();
        out.println(3 * r * r);
    }

    static class MyScanner {

        BufferedReader br;
        StringTokenizer st;

        MyScanner(FileReader fileReader) {
            br = new BufferedReader(fileReader);
        }

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

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

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

        char nc() {
            return nn().charAt(0);
        }

        int ni() {
            return Integer.parseInt(nn());
        }

        long nl() {
            return Long.parseLong(nn());
        }

        double nd() {
            return Double.parseDouble(nn());
        }

        int[] niArr0(int n) {
            int[] ar = new int[n];
            for (int i = 0; i < n; i++) {
                ar[i] = ni();
            }
            return ar;
        }

        int[] niArr1(int n) {
            int[] ar = new int[n + 1];
            for (int i = 1; i <= n; i++) {
                ar[i] = ni();
            }
            return ar;
        }

        long[] nlArr0(int n) {
            long[] ar = new long[n];
            for (int i = 0; i < n; i++) {
                ar[i] = nl();
            }
            return ar;
        }

        long[] nlArr1(int n) {
            long[] ar = new long[n + 1];
            for (int i = 1; i <= n; i++) {
                ar[i] = nl();
            }
            return ar;
        }
    }
}

Compiler output:
a.cc:1:1: error: 'import' does not name a type
    1 | import com.sun.deploy.ui.MacJavaTrayIcon;
      | ^~~~~~
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 com.sun.tools.hat.internal.model.ReachableExcludes;
      | ^~~~~~
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 jdk.nashorn.internal.runtime.WithObject;
      | ^~~~~~
a.cc:3:1: note: C++20 'import' only available with '-fmodules-ts'
a.cc:5:1: error: 'import' does not name a type
    5 | import javax.swing.text.AsyncBoxView;
      | ^~~~~~
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.*;
      | ^~~~~~
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.math.BigInteger;
      | ^~~~~~
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.util.*;
      | ^~~~~~
a.cc:8:1: note: C++20 'import' only available with '-fmodules-ts'
a.cc:12:12: error: expected ':' before 'static'
   12 |     private static PrintWriter out;
      |            ^~~~~~~
      |            :
a.cc:12:20: error: 'PrintWriter' does not name a type
   12 |     private static PrintWriter out;
      |                    ^~~~~~~~~~~
a.cc:14:12: error: expected ':' before 'static'
   14 |     private static <T> void mprintln(T... ar) {
      |            ^~~~~~~
      |            :
a.cc:14:20: error: expected unqualified-id before '<' token
   14 |     private static <T> void mprintln(T... ar) {
      |                    ^
a.cc:21:11: error: expected ':' before 'static'
   21 |     public static void main(String[] args) throws FileNotFoundException {
      |           ^~~~~~~
      |           :
a.cc:21:29: error: 'String' has not been declared
   21 |     public static void main(String[] args) throws FileNotFoundException {
      |                             ^~~~~~
a.cc:21:38: error: expected ',' or '...' before 'args'
   21 |     public static void main(String[] args) throws FileNotFoundException {
      |                                      ^~~~
a.cc:21:42: error: expected ';' at end of member declaration
   21 |     public static void main(String[] args) throws FileNotFoundException {
      |                                          ^
      |                                           ;
a.cc:21:44: error: 'throws' does not name a type
   21 |     public static void main(String[] args) throws FileNotFoundException {
      |                                            ^~~~~~
a.cc:44:12: error: 'final' does not name a type
   44 |     static final long MOD = (long) (1e9 + 7);
      |            ^~~~~
a.cc:46:12: error: expected ':' before 'static'
   46 |     private static void getAns(MyScanner sc) {
      |            ^~~~~~~
      |            :
a.cc:46:32: error: 'MyScanner' has not been declared
   46 |     private static void getAns(MyScanner sc) {
      |                                ^~~~~~~~~
a.cc:53:9: error: 'BufferedReader' does not name a type
   53 |         BufferedReader br;
      |         ^~~~~~~~~~~~~~
a.cc:54:9: error: 'StringTokenizer' does not name a type
   54 |         StringTokenizer st;
      |         ^~~~~~~~~~~~~~~
a.cc:56:29: error: expected ')' before 'fileReader'
   56 |         MyScanner(FileReader fileReader) {
      |                  ~          ^~~~~~~~~~~
      |                             )
a.cc:64:9: error: 'String' does not name a type
   64 |         String nn() {
      |         ^~~~~~
a.cc:75:9: error: 'String' does not name a type
   75 |         String nextLine() {
      |         ^~~~~~
a.cc:101:12: error: expected unqualified-id before '[' token
  101 |         int[] niArr0(int n) {
      |            ^
a.cc:109:12: error: expected unqualified-id before '[' token
  109 |         int[] niArr1(int n) {
      |            ^
a.cc:117:13: error: expected unqualified-id before '[' token
  117 |         long[] nlArr0(int n) {
      |             ^
a.cc:125:13: error: expected unqualified-id before '[' token
  125 |         long[] nlArr1(int n) {
      |             ^
a.cc:132:6: error: expected ';' after class definition
  132 |     }
      |      ^
      |      ;
a.cc:51:5: error: a storage class can only be specified for objects and functions
   51 |     static class MyScanner {
      |     ^~~~~~
a.cc:133:2: error: expected ';' after class definition
  133 | }
      |  ^
      |  ;
a.cc: In static member function 'static void Main::getAns(int)':
a.cc:47:21: error: request for member 'nl' in 'sc', which is of non-class type 'int'
   47 |         long r = sc.nl();
      |                     ^~
a.cc:48:9: error: 'out' was not declared in this scope
   48 |         out.println(3 * r * r);
      |         ^~~
a.cc: In constructor 'Main::MyScanner::MyScanner()':
a.cc:61:13: error: 'br' was not declared in this scope
   61 |             br = new BufferedReader(new InputStreamReader(System.in));
      |             ^~
a.cc:61:22: error: expected type-specifier before 'BufferedReader'
   61 |             br = new BufferedReader(new InputStreamReader(System.in));
      |                      ^~~~~~~~~~~~~~
a.cc: In member function 'char Main::MyScanner::nc()':
a.cc:86:20: error: 'nn' was not declared in this scope; did you mean 'nc'?
   86 |             return nn().charAt(0);
      |                    ^~
      |                    nc
a.cc: In member function 'int Main::MyScanner::ni()':
a.cc:90:20: error: 'Integer' was not declared in this scope
   90 |             return Integer.parseInt(nn());
      |                    ^~~~~~~
a.cc:90:37: error: 'nn' was not declared in this scope; did you mean 'nc'?
   90 |             return Integer.parseInt(nn());
      |                                     ^~
      |                                     nc
a.cc: In member function 'long int Main::MyScanner::nl()':
a.cc:94:20: error: 'Long' was not declared in this scope; did you mean 'long'?
   94 |             return Long.parseLong(nn());
      |                    ^~~~
      |                    long
a.cc:94:35: error: 'nn' was not declared in this scope; did you mean 'nc'?
   94 |             return Long.parseLong(nn());
      |                                   ^~
      |                                   nc
a.cc: In member function 'double Main::MyScanner::nd()':
a.cc:98:20: error: 'Double' was not declared in this scope; did you mean 'double'?
   98 |             return Double.parseDouble(nn());
      |                    ^~~~~~
      |                    double
a.cc:98:39: error: 'nn' was not declared in this scope; did you mean 'nc'?
   98 |             return Double.parseDouble(nn());
      |                                       ^~
      |                                       nc