Language: C++

using System;
using System.Collections.Generic;
using System.Linq;
class Program
{
    public static bool f = false, t = true;
    static void Main(string[] args)
    {
        Console.WriteLine(48-int.Parse(Read.Str()));
    }
    public static long gcd(long a, long b)
    {
        while (true)
        {
            if (a == 0) { return b; }
            if (b == 0) { return a; }
            if (a > b) { a -= b; }
            else { b -= a; }
        }
    }
    public static long lcm(long a, long b) { return a / gcd(a, b) * b; }
    public static bool IsPrime(int num)
    {
        if (num < 2) return false;
        else if (num == 2) return true;
        else if (num % 2 == 0) return false; // 偶数はあらかじめ除く

        double sqrtNum = Math.Sqrt(num);
        for (int i = 3; i <= sqrtNum; i += 2)
        {
            if (num % i == 0)
            {
                // 素数ではない
                return false;
            }
        }

        // 素数である
        return true;
    }
}
public static class Read
{
    public static void outl(string n = "") { Console.WriteLine(n); return; }
    public static long Long() { return long.Parse(Console.ReadLine()); }
    public static long[] longs() { return Console.ReadLine().Split().Select(long.Parse).ToArray(); }
    public static int Int() { return int.Parse(Console.ReadLine()); }
    public static int[] ints() { return Console.ReadLine().Split().Select(int.Parse).ToArray(); }
    public static string Str() { return Console.ReadLine(); }
    public static string[] Strs() { return Console.ReadLine().Split(); }
}

Compiler output:
a.cc:1:7: error: expected nested-name-specifier before 'System'
    1 | using System;
      |       ^~~~~~
a.cc:2:7: error: expected nested-name-specifier before 'System'
    2 | using System.Collections.Generic;
      |       ^~~~~~
a.cc:3:7: error: expected nested-name-specifier before 'System'
    3 | using System.Linq;
      |       ^~~~~~
a.cc:6:11: error: expected ':' before 'static'
    6 |     public static bool f = false, t = true;
      |           ^~~~~~~
      |           :
a.cc:6:24: error: ISO C++ forbids in-class initialization of non-const static member 'Program::f'
    6 |     public static bool f = false, t = true;
      |                        ^
a.cc:6:35: error: ISO C++ forbids in-class initialization of non-const static member 'Program::t'
    6 |     public static bool f = false, t = true;
      |                                   ^
a.cc:7:22: error: 'string' has not been declared
    7 |     static void Main(string[] args)
      |                      ^~~~~~
a.cc:7:31: error: expected ',' or '...' before 'args'
    7 |     static void Main(string[] args)
      |                               ^~~~
a.cc:11:11: error: expected ':' before 'static'
   11 |     public static long gcd(long a, long b)
      |           ^~~~~~~
      |           :
a.cc:21:11: error: expected ':' before 'static'
   21 |     public static long lcm(long a, long b) { return a / gcd(a, b) * b; }
      |           ^~~~~~~
      |           :
a.cc:22:11: error: expected ':' before 'static'
   22 |     public static bool IsPrime(int num)
      |           ^~~~~~~
      |           :
a.cc:41:2: error: expected ';' after class definition
   41 | }
      |  ^
      |  ;
a.cc: In static member function 'static void Program::Main(int*)':
a.cc:9:9: error: 'Console' was not declared in this scope
    9 |         Console.WriteLine(48-int.Parse(Read.Str()));
      |         ^~~~~~~
a.cc:9:30: error: expected primary-expression before 'int'
    9 |         Console.WriteLine(48-int.Parse(Read.Str()));
      |                              ^~~
a.cc: In static member function 'static bool Program::IsPrime(int)':
a.cc:28:26: error: 'Math' was not declared in this scope
   28 |         double sqrtNum = Math.Sqrt(num);
      |                          ^~~~
a.cc: At global scope:
a.cc:42:1: error: expected unqualified-id before 'public'
   42 | public static class Read
      | ^~~~~~