using System;
using System.IO;

namespace Sandbox
{
    internal class Program
    {
        private static void Main(string[] args)
        {
            var scanner = new Scanner();
            var a = scanner.GetNextAsLong();
            var b = scanner.GetNextAsLong();
            var c = scanner.GetNextAsLong();
            var d = scanner.GetNextAsLong();
            var result = 0L;

            if (d > c)
            {
                var tmp = d;
                d = c;
                c = tmp;
            }

            var countAforC = (a - 1) / c;
            var countAforD = (a - 1) / d;
            var countBforC = b / c;
            var countBforD = b / d;

            if (c == d)
            {
                result = (b - a + 1) - (countBforC - countAforC);
                Console.WriteLine(result);
                return;
            }

            if (c % d == 0)
            {
                result = (b - a + 1) - (countBforD - countAforD);
                Console.WriteLine( result);
                return;
            }

            var gcd = MathEx.Lcm(c, d);

            var countAforCD = (a - 1) / gcd;
            var countBforCD = b / gcd;

            var countB = countBforC + countBforD - countBforCD;
            var countA = countAforC + countAforD - countAforCD;
            result = (b - a + 1) - (countB - countA);

            Console.WriteLine(result);
        }

        #region GCD LCM
    /// <summary>
    /// 様々な数学的関数の静的メソッドを提供します．
    /// </summary>
    public static partial class MathEx {
        /// <summary>
        /// 2 つの整数の最大公約数を求めます．
        /// </summary>
        /// <param name="n">最初の値</param>
        /// <param name="m">2 番目の値</param>
        /// <returns>2 つの整数の最大公約数</returns>
        /// <remarks>ユークリッドの互除法に基づき最悪計算量 O(log N) で実行されます．</remarks>
        public static int Gcd(int n, int m) { return (int)Gcd((long)n, m); }

        /// <summary>
        /// 2 つの整数の最大公約数を求めます．
        /// </summary>
        /// <param name="n">最初の値</param>
        /// <param name="m">2 番目の値</param>
        /// <returns>2 つの整数の最大公約数</returns>
        /// <remarks>ユークリッドの互除法に基づき最悪計算量 O(log N) で実行されます．</remarks>
        public static long Gcd(long n, long m) {
            n = Math.Abs(n);
            m = Math.Abs(m);
            while (n != 0)
            {
                m %= n;
                if (m == 0)
                {
                    return n;
                }

                n %= m;
            }
            return m;
        }

        /// <summary>
        /// 2 つの整数の最小公倍数を求めます．
        /// </summary>
        /// <param name="n">最初の値</param>
        /// <param name="m">2 番目の値</param>
        /// <returns>2 つの整数の最小公倍数</returns>
        /// <remarks>最悪計算量 O(log N) で実行されます．</remarks>
        public static long Lcm(long n, long m) { return (n / Gcd(n, m)) * m; }
    }
    #endregion
        #region String Scanner

        public class Scanner
        {
            private const char Separator = ' ';
            private readonly StreamReader _Stream = new StreamReader(Console.OpenStandardInput());
            private int _Pos;
            private string[] _Line = new string[0];

            #region get a element

            public string GetNext()
            {
                // ReSharper disable once InvertIf
                if (this._Pos >= this._Line.Length)
                {
                    // ReSharper disable once PossibleNullReferenceException
                    this._Line = this._Stream.ReadLine().Split(Separator);
                    this._Pos = 0;
                }

                return this._Line[this._Pos++];
            }

            public int GetNextAsInt()
            {
                return int.Parse(this.GetNext());
            }

            public long GetNextAsLong()
            {
                return long.Parse(this.GetNext());
            }

            public double GetNextAsDouble()
            {
                return double.Parse(this.GetNext());
            }

            #endregion

            #region get array

            public string[] ToArrayFromNextLine()
            {
                if (this._Pos >= this._Line.Length)
                {
                    // ReSharper disable once PossibleNullReferenceException
                    this._Line = this._Stream.ReadLine().Split(Separator);
                }

                this._Pos = this._Line.Length;
                return this._Line;
            }

            public int[] ToIntArrayFromNextLine()
            {
                return ToIntArray(this.ToArrayFromNextLine());
            }

            public long[] ToLongArrayFromNextLine()
            {
                return ToLongArray(this.ToArrayFromNextLine());
            }

            public double[] ToDoubleArrayFromNextLine()
            {
                return ToDoubleArray(this.ToArrayFromNextLine());
            }

            #endregion

            #region convert array

            private static int[] ToIntArray(string[] array)
            {
                var result = new int[array.Length];
                for (var i = 0; i < array.Length; i++)
                {
                    result[i] = int.Parse(array[i]);
                }

                return result;
            }

            private static long[] ToLongArray(string[] array)
            {
                var result = new long[array.Length];
                for (var i = 0; i < array.Length; i++)
                {
                    result[i] = long.Parse(array[i]);
                }

                return result;
            }

            private static double[] ToDoubleArray(string[] array)
            {
                var result = new double[array.Length];
                for (var i = 0; i < array.Length; i++)
                {
                    result[i] = double.Parse(array[i]);
                }

                return result;
            }

            #endregion
        }

        #endregion
    }
}


Measured memory_bytes: 13140