Language: C++

using System;
using System.Text;
using System.Linq;
using System.Collections;
using System.Collections.Generic;
using static System.Console;
using static System.Math;

namespace AtCoder
{
    public class Program
    {
        public static void Main(string[] args)
        {
            new Program().Solve(new ConsoleInput(Console.In, ' '));
        }

        public void Solve(ConsoleInput cin)
        {
            var nums = cin.ReadLongArray(4);
            var A = nums[0];
            var B = nums[1];
            var C = nums[2];
            var D = nums[3];
            var muls = countMuls(A, B, C) + countMuls(A, B, D) - countMuls(A, B, C * D / gcd(C, D));
            Console.WriteLine(B - A + 1 - muls);
        }

        static long countMuls(long a, long b, long k)
        {
            return b / k - (a - 1) / k;
        }

        static long gcd(long a, long b)
        {
            return b == 0 ? a : gcd(b, a % b);
        }
    }

    public class ConsoleInput
    {
        private readonly System.IO.TextReader _stream;
        private char _separator = ' ';
        private Queue<string> inputStream;
        public ConsoleInput(System.IO.TextReader stream, char separator = ' ')
        {
            this._separator = separator;
            this._stream = stream;
            inputStream = new Queue<string>();
        }
        public string Read
        {
            get
            {
                if (inputStream.Count != 0) return inputStream.Dequeue();
                string[] tmp = _stream.ReadLine().Split(_separator);
                for (int i = 0; i < tmp.Length; ++i)
                    inputStream.Enqueue(tmp[i]);
                return inputStream.Dequeue();
            }
        }
        public string ReadLine { get { return _stream.ReadLine(); }}
        public int ReadInt { get { return int.Parse(Read); }}
        public long ReadLong { get { return long.Parse(Read); }}
        public double ReadDouble { get { return double.Parse(Read); }}
        public string[] ReadStrArray(long N) { var ret = new string[N]; for (long i = 0; i < N; ++i) ret[i] = Read; return ret;}
        public int[] ReadIntArray(long N) { var ret = new int[N]; for (long i = 0; i < N; ++i) ret[i] = ReadInt; return ret;}
        public long[] ReadLongArray(long N) { var ret = new long[N]; for (long i = 0; i < N; ++i) ret[i] = ReadLong; return ret;}
    }
}


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.Text;
      |       ^~~~~~
a.cc:3:7: error: expected nested-name-specifier before 'System'
    3 | using System.Linq;
      |       ^~~~~~
a.cc:4:7: error: expected nested-name-specifier before 'System'
    4 | using System.Collections;
      |       ^~~~~~
a.cc:5:7: error: expected nested-name-specifier before 'System'
    5 | using System.Collections.Generic;
      |       ^~~~~~
a.cc:6:7: error: expected nested-name-specifier before 'static'
    6 | using static System.Console;
      |       ^~~~~~
a.cc:7:7: error: expected nested-name-specifier before 'static'
    7 | using static System.Math;
      |       ^~~~~~
a.cc:11:5: error: expected unqualified-id before 'public'
   11 |     public class Program
      |     ^~~~~~
a.cc:40:5: error: expected unqualified-id before 'public'
   40 |     public class ConsoleInput
      |     ^~~~~~